Magnetic field sensor having a temperature compensated threshold on power up

ABSTRACT

A magnetic field sensor includes one or more magnetic field sensing elements configured to generate a magnetic field signal responsive to a magnetic field and a detector coupled to receive an interpolated threshold and a signal representative of the magnetic field signal, wherein the detector is configured to compare the interpolated threshold with the signal representative of the magnetic field signal to generate a detector output signal. A memory is configured to store a first threshold value indicative of a threshold value at a first temperature and a second threshold value indicative of a threshold value at a second temperature lower than the first temperature and a threshold module coupled to the memory and configured to generate the interpolated threshold based on the stored first and second threshold values.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-in-Part and claims the benefit of U.S. patent application Ser. No. 15/132,642 filed Apr. 19, 2016 which application is a Continuation Application of and claims the benefit of U.S. patent application Ser. No. 13/833,847 filed Mar. 15, 2013 and issued as U.S. Pat. No. 9,395,391 on Jul. 19, 2016, all of which are incorporated herein by reference in their entirety. This application is also a Continuation-in-Part and claims the benefit of U.S. application Ser. No. 15/466,894 filed Mar. 23, 2017 which application is a Continuation Application of and claims the benefit of U.S. patent application Ser. No. 14/250,574 filed Apr. 11, 2014 and issued as U.S. Pat. No. 9,644,999 on May 9, 2017, which application is a Continuation of and claims the benefit of U.S. patent application Ser. No. 13/345,021 filed Jan. 6, 2012 and issued as U.S. Pat. No. 8,736,260 on May 27, 2014 all of which are incorporated herein by reference in their entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable.

FIELD

This invention relates generally to magnetic field sensors for sensing a rotation or a movement of an object and, more particularly, to a magnetic field sensor that utilizes a temperature compensated threshold.

BACKGROUND

Various types of magnetic field sensing elements are known, including Hall Effect elements and magnetoresistance elements. Magnetic field sensors generally include a magnetic field sensing element and other electronic components. Some magnetic field sensors also include a fixed permanent magnet.

Magnetic field sensors provide an electrical signal representative of a sensed magnetic field, or, in some embodiments, fluctuations of a magnetic field associated with the permanent magnet. In the presence of a moving ferromagnetic object (e.g., a gear, a ring magnet, or a linear multi-pole magnet), the magnetic field sensed by the magnetic field sensor can vary in accordance with a shape or profile of the moving ferromagnetic object.

Magnetic field sensors are often used to detect movement of features of a ferromagnetic target, such as a gear with gear teeth and/or gear slots. A magnetic field sensor in this application is commonly referred to as a “gear tooth” sensor.

In some arrangements, the gear is placed upon a target object, for example, a camshaft in an engine or on a shaft of a motor as examples, thus the rotation of the target object (e.g., camshaft or more generally shaft) is sensed by detection of the moving features of the gear. Gear tooth sensors can be used in automotive applications, for example, to provide information to an engine control processor for ignition timing control, fuel management, and other operations. Gear tooth sensors can also be used in other applications such as in motor control applications to provide information to an electronic control unit.

Information provided by the gear tooth sensor to the engine control processor can include, but is not limited to, an absolute angle of rotation of a target object (e.g., a camshaft) as it rotates, and a direction of rotation. With this information, the engine control processor can adjust the timing of firing of the ignition system and the timing of fuel injection by the fuel injection system. Thus, it will be recognized that accurate information about the angle of rotation is important for proper engine operation.

Gear tooth sensors can also be used in other applications, including, but not limited to, anti-lock braking systems and in transmissions.

Many types of magnetic field sensors may not provide an accurate output signal (e.g., indication of absolute angle of rotation of an object) immediately upon power up of the magnetic field sensor, and/or immediately upon movement of the target object from zero rotating speed, and/or upon movement slowing to zero rotating speed, but instead provide an accurate output signal only once the magnetic field sensor has been powered up for a period of time, and the target object has moved through a substantial rotation or is moving with substantial speed.

The above accurate output signal refers to accuracy of the positions of transition edges (corresponding to gear teeth edges, ring magnet pole edges, or linear multi-pole magnet pole edges) in the output signal from the magnetic field sensor.

In general, a so-called “precision” rotation detector can provide an accurate output signal only after some period following power up of the magnetic field sensor and after the gear has been rotating for some period of time. In contrast, in general, a so-called “true power on state” (TPOS) detector can provide a reasonably accurate output signal, but less accurate than the precision rotation detector, at an earlier time after the magnetic field sensor powers up and at an earlier time after the gear starts rotating.

One type of precision rotation detector is described in U.S. Pat. No. 6,525,531, issued Feb. 25, 2003. This precision rotation detector includes a positive digital-to-analog converter (PDAC) and a negative digital-to-analog converter (NDAC) that track positive and negative peaks of magnetic field signal, respectively, for use in generating a threshold signal. A varying magnetic field signal is compared to the threshold signal. However, the outputs of the PDAC and the NDAC may not provide accurate indications of the positive and negative peaks of the magnetic field signal until several cycles of the signal (i.e., signal peaks) occur (i.e., until several gear teeth have passed). Other types of precision rotation detectors are described, for example, in U.S. Pat. No. 7,199,579, issued Apr. 2, 2007, U.S. Pat. No. 7,368,904, issued Apr. 6, 2008, U.S. Pat. No. 6,297,627, issued Oct. 2, 2001, and U.S. Pat. No. 5,917,320, issued Jun. 29, 1999, each of which is incorporated herein by reference, and each of which is assigned to the assignee of the present invention.

A conventional TPOS detector is described in U.S. Pat. No. 7,362,094, issued Apr. 22, 2008. Some conventional TPOS detectors simply compare a magnetic field signal with a fixed, predetermined, and sometimes trimmed, threshold.

A TPOS detector can be used in conjunction with a precision rotation detector, both providing information to the engine control processor. A TPOS detector can be combined in the same integrated circuit with a precision rotation detector, and the magnetic field sensor after power up, can first use the TPOS detector and then switch to use the precision rotation detector.

As described above, the conventional TPOS detector provides a reasonably accurate output signal with only a small initial rotation of the target object, and before the precision rotation detector can provide an accurate output signal. Furthermore, the TPOS detector can provide information about whether it is proximate to a gear tooth or a gear valley nearly immediately upon power up.

A TPOS detector can provide information to the engine control processor that can be more accurate than information provided by the precision rotation detector at times proximate to the time of power up of the magnetic field sensor, and also at times near the beginning and end of rotation of the target object (e.g., start and stop of the engine and camshaft). However, the TPOS detector may be less accurate than the precision rotation detector at some time after the magnetic field sensor has powered up and when the object is rotating at full speed. When the object is rotating at full speed, the engine control processor can primarily use rotation information provided by the precision rotation detector.

As described above, unlike the precision rotation detector, the conventional TPOS detector has a fixed predetermined threshold against which a magnetic field signal is compared. An output signal from a conventional TPOS detector has two states, typically a high and a low state, in accordance with features on the target object.

It is known that various parameters affect a magnitude of the magnetic field signal generated by the TPOS magnetic field sensor. For example, temperature is known to affect a sensitivity of the Hall element, and therefore, a magnitude of the magnetic field signal. Changes in size of an air gap between the TPOS magnetic field sensor and the TPOS cam or gear can also affect a magnitude of the magnetic field signal.

In a TPOS detector, when the magnetic field signal is compared against a fixed predetermined threshold, the changes in the amplitude of the magnetic field signal due to temperature, air gap, etc., can cause undesirable changes in positions of the edges in the above-described output signal from the TPOS detector. A conventional TPOS detector can have a comparator therein operating as a comparator detector.

Some sensors monitor properties by detecting a magnetic field associated with proximity or movement of a target object with respect to one or more magnetic field sensing elements. In magnetic field sensors including multiple magnetic field sensing elements, magnetic field signals from the sensing elements can be processed by separate processing channels to generate respective phase separated signals. One such magnetic field sensor is the Allegro MicroSystems, LLC ATS605LSG Dual Output Differential Speed and Direction Sensor IC, in which the output signals from each of the processing channels are provided at respective output pins of the sensor integrated circuit (IC). In an automotive application, the sensor IC output signals can be coupled to an engine control unit (ECU) for further processing, such as detection of gear or wheel speed, direction and/or vibration. More generally, the sensor IC output signals can be coupled to an electronic control unit.

SUMMARY

A magnetic field sensor includes one or more magnetic field sensing elements configured to generate a magnetic field signal responsive to a magnetic field and a detector coupled to receive an interpolated threshold and a signal representative of the magnetic field signal, wherein the detector is configured to compare the interpolated threshold with the signal representative of the magnetic field signal to generate a detector output signal. A memory is configured to store a first threshold value indicative of a threshold value at a first temperature and a second threshold value indicative of a threshold value at a second temperature lower than the first temperature and a threshold module coupled to the memory and configured to generate the interpolated threshold based on the stored first and second threshold values.

Features may include one or more of the following alone or in combination. The sensor may include a temperature sensor to generate a temperature signal indicative of the sensor temperature and the threshold module can be further responsive to the temperature signal to generate the interpolated threshold.

The sensor can include two or more comparator detectors, each providing a respective detector output signal for use upon sensor power up to generate a direction signal indicative of a direction of motion of a target positioned to affect the magnetic field.

The stored first and second threshold values can be updated periodically and/or at predetermined update times, such as when a dynamic threshold (as may be based on tracked peaks and valleys of the magnetic field signal) differs from the interpolated threshold by a more than a predetermined amount. Updating the first and second stored threshold values can include use of a weighting factor.

Also described is a method of sensing a magnetic field with a magnetic field sensor, including generating a magnetic field signal responsive to the magnetic field and storing, in a non-volatile memory device, a first threshold value indicative of a threshold value at a first temperature and a second threshold value indicative of a threshold value at a second temperature lower than the first temperature. An interpolated threshold is generated based on the first stored threshold value and the second stored threshold value and the interpolated threshold is compared with a signal representative of the magnetic field signal to generate a detector output signal.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features of the invention, as well as the invention itself may be more fully understood from the following detailed description of the drawings, in which:

FIG. 1 is a block diagram showing a magnetic field sensor having a comparator detector in the form of a “true power on state” (TPOS) detector and a “precision rotation” detector, which is proximate to a gear having gear features, the gear disposed upon a shaft configured to rotate, i.e., upon a target object;

FIG. 2 is a graph showing a magnetic field signal and showing an exemplary calculated threshold and an exemplary predetermined threshold that can be compared with the magnetic field signal within the TPOS detector of FIG. 1;

FIG. 3 is a graph showing signals resulting from the comparisons of FIG. 2;

FIG. 4 is a block diagram showing a magnetic field sensor used to sense rotation of a gear, having a segment processor configured to correct gain and/or offset variations versus temperature, and also having a rotation module to provide and output signal indicative of rotation of the gear;

FIG. 5 is a graph showing an exemplary characteristic curve of sensitivity versus temperature of a magnetic field sensor and showing gain correction coefficients;

FIG. 6 is a graph showing an exemplary characteristic curve of offset versus temperature of a magnetic field sensor and showing offset correction coefficients;

FIG. 7 is a flow chart showing a process to correct gain and/or offset versus temperature of the magnetic field sensor of FIG. 4.

FIG. 8 is a block diagram showing further details of the rotation module of the magnetic field sensor of FIG. 4 and showing a threshold module;

FIG. 9 is a block diagram showing an exemplary threshold module that can be used as the threshold module of FIG. 8 and having a measured threshold module to generate a measured threshold value and a memory device to store the measured threshold value;

FIG. 10 is a flowchart showing an exemplary process for using a magnetic field sensor having the threshold module of FIG. 9;

FIG. 11 is graph representing functions of the measured threshold module of FIG. 9;

FIG. 12 is a block diagram showing a magnetic field sensor;

FIG. 13 is a block diagram showing further details of the rotation module of the magnetic field sensor of FIG. 12 and showing a threshold module;

FIG. 14 is a block diagram showing an exemplary threshold module that can be used as the threshold module of FIG. 13 and having a measured threshold module to generate a measured threshold value and a memory device to store the measured threshold value;

FIG. 15 is a flowchart showing an exemplary process for using a magnetic field sensor having the threshold module of FIG. 14; and

FIG. 16 illustrates signals associated with direction detection.

DETAILED DESCRIPTION

Before describing the present invention, some introductory concepts and terminology are explained. As used herein, the term “magnetic field sensing element” is used to describe a variety of electronic elements that can sense a magnetic field. The magnetic field sensing element can be, but is not limited to, a Hall Effect element, a magnetoresistance element, or a magnetotransistor. As is known, there are different types of Hall Effect elements, for example, a planar Hall element, a vertical Hall element, and a Circular Vertical Hall (CVH) element. As is also known, there are different types of magnetoresistance elements, for example, a semiconductor magnetoresistance element such as Indium Antimonide (InSb), a giant magnetoresistance (GMR) element, an anisotropic magnetoresistance element (AMR), a tunneling magnetoresistance (TMR) element, and a magnetic tunnel junction (MTJ). The magnetic field sensing element may be a single element or, alternatively, may include two or more magnetic field sensing elements arranged in various configurations, e.g., a half bridge or full (Wheatstone) bridge. Depending on the device type and other application requirements, the magnetic field sensing element may be a device made of a type IV semiconductor material such as Silicon (Si) or Germanium (Ge), or a type III-V semiconductor material like Gallium-Arsenide (GaAs) or an Indium compound, e.g., Indium-Antimonide (InSb).

The above-described “circular vertical Hall” (CVH) sensing element, another type of magnetic field sensing element, which includes a plurality of vertical magnetic field sensing elements, is known and described in PCT Patent Application No. PCT/EP2008056517, entitled “Magnetic Field Sensor for Measuring Direction of a Magnetic Field in a Plane,” filed May 28, 2008, and published in the English language as PCT Publication No. WO 2008/145662, which application and publication thereof are incorporated by reference herein in their entirety. The CVH sensing element includes a circular arrangement of vertical Hall elements arranged over a common circular implant region (e.g., epitaxial region) in a substrate. The CVH sensing element can be used to sense a direction (and optionally a strength) of a magnetic field in a plane of the substrate.

As is known, some of the above-described magnetic field sensing elements tend to have an axis of maximum sensitivity parallel to a substrate that supports the magnetic field sensing element, and others of the above-described magnetic field sensing elements tend to have an axis of maximum sensitivity perpendicular to a substrate that supports the magnetic field sensing element. In particular, planar Hall elements tend to have axes of sensitivity perpendicular to a substrate, while metal based or metallic magnetoresistance elements (e.g., GMR, TMR, AMR) and vertical Hall elements tend to have axes of sensitivity parallel to a substrate.

As used herein, the term “magnetic field sensor” is used to describe a circuit that uses a magnetic field sensing element, generally in combination with other circuits. Magnetic field sensors are used in a variety of applications, including, but not limited to, an angle sensor that senses an angle of a direction of a magnetic field, a current sensor that senses a magnetic field generated by a current carried by a current-carrying conductor, a magnetic switch that senses the proximity of a ferromagnetic object, a rotation detector that senses passing ferromagnetic articles, for example, magnetic domains of a ring magnet, and a magnetic field sensor that senses a magnetic field density of a magnetic field.

While exemplary circuits and methods are described below that use a Hall Effect element, in other embodiments, the same or similar techniques can be used in conjunction with another type of magnetic field sensing element.

Rotation detector types of magnetic field sensors are shown and described in examples, below. However, the same or similar techniques can be applied to any magnetic field sensor, and, desirably, to any magnetic field sensor that experiences temperature excursions and for which it is desirable to store a threshold when the magnetic field sensor is powered off.

Referring to FIG. 1, an exemplary magnetic field sensor arrangement 10 includes a magnetic field sensor 12. The magnetic field sensor 12 includes a magnetic field sensing circuit 14 having a magnetic field sensing element 16 coupled to an electronic circuit 18. The electronic circuit 18 can include a comparator detector 18, which, in some embodiments, can be a true power on state (TPOS) detector 18 a, and a precision rotation detector 18 b, both of which are described more fully below.

The magnetic field sensor 12 can also include a magnet 20. The magnet 20 is configured to generate a magnetic field directed along an axis 22. The electronic circuit 18 is configured to generate an output signal 24, which is generated by the TPOS detector 18 a for a time period near to a start up of the magnetic field sensor 12, and which can be generated by the precision rotation detector thereafter.

The magnetic field sensor arrangement 10 can also include a target 26 (e.g., cam or gear) having features 26 a, 26 b, 26 c, 26 d. The cam 26 can be disposed, for example, upon a shaft 30 (i.e., a target object) configured to rotate in a direction 32. Cam 26 and other target objects described herein can have a variety of forms, including, but not limited to, a ring magnet having one or more pole pair, and a gear having two or more gear teeth. Ferromagnetic gears are used in some examples below to show a rotating ferromagnetic object having ferromagnetic features, i.e., teeth. However, in other embodiments, the gear can be replaced with a ring magnet having at least one pole pair. Also, linear arrangements of ferromagnetic objects are possible that move linearly.

In operation, as the cam 26 rotates, the cam features 26 a, 26 b, 26 c, 26 d interrupt the magnetic field generated by the magnet 20. Interruptions of the magnetic field generated by the magnet 20 are sensed by the magnetic field sensing element 16 and result in state transitions in the output signal 24.

Particular arrangement and spacing of the cam features 26 a, 26 b, 26 c, 26 d results in the TPOS detector 18 a being able to provide the TPOS output signal 24 having transitions after only a small number of degrees of rotation of the TPOS cam 26, which, in some embodiments, can be interpreted by a control computer to generate an absolute angle of rotation of the cam 26 and of the shaft 30 upon which the cam 26 is disposed.

Furthermore, by circuits and techniques described below, the TPOS detector 18 a can provide an indication of whether the magnetic field sensor 12 is proximate to a gear tooth or a gear valley at the time of power up of the magnetic field sensor 12.

Referring now to FIG. 2, a graph 50 has a horizontal axis with a scale in units of target object rotation angle, for example, from 0 to 360 degrees. The graph 50 also includes a vertical axis having a scale with units of volts in arbitrary units. A signal 52 can be the same as or similar to a magnetic field signal generated within the magnetic field sensor 12 of FIG. 1, for example, in conjunction with the magnetic field sensing element 16. It should be appreciated that the high state periods of the signal 52 correspond to the features 26 a, 26 b, 26 c, 26 d of the cam 26 of FIG. 1 as they pass by the magnetic field sensing element 16 of FIG. 1 as the cam 26 rotates.

The magnetic field signal 52 is shown in analog form having continuous analog values, but can equivalently be a signal having discrete digital values comparable to sampled ones of the analog values. While the signal 52 is indicated to be a voltage signal, in some other embodiments, the signal 52 is a current signal.

A predetermined threshold 54 is shown and further described below in conjunction with FIG. 3. The predetermined threshold 54 is similar to that which is used in a conventional TPOS detector. A comparator threshold 56, calculated (at different respective times) in accordance with one of a plurality of stored measured threshold is also shown and further described below in conjunction with FIG. 3. The comparator threshold 56, calculated in accordance with one of the plurality of stored measured threshold values, is not used by a conventional TPOS detector.

As used herein, the terms “comparator threshold” and “TPOS threshold” are used to mean essentially the same threshold. It should be understood that a so-called “comparator” can be comprised of an analog comparator having a two state output signal indicative of an input signal being above or below a threshold level (or indicative of one input signal being above or below another input signal). However the comparator can also be comprised of a digital circuit having an output signal with at least two states indicative of an input signal being above or below a threshold level (or indicative of one input signal being above or below another input signal), respectively, or a digital value above or below a digital threshold value (or another digital value), respectively.

As used herein, the term “predetermined,” when referring to a value or signal, is used to refer to a value or signal that is set, or fixed, in the factory at the time of manufacture, or by external means, e.g., programming, thereafter. As used herein, the term “determined,” when referring to a value or signal, is used to refer to a value or signal that is identified by a circuit during operation, after manufacture.

Referring now to FIG. 3, a graph 70 has a horizontal axis with a scale in units of target object rotation angle, for example, from 0 to 360 degrees. The graph 70 also includes a vertical axis having a scale with units of volts in arbitrary units.

A signal 74 has two states, positions of transitions between which are determined by crossings of the signal 52 of FIG. 2 above and below the predetermined threshold 54. A signal 72 has two states, positions of transitions between which are determined by crossings of the signal 52 of FIG. 2 above and below the calculated threshold 56. Accordingly, it can be seen that changes in the position, i.e., the value, of the threshold used to compare against the signal 52 of FIG. 2, affects positions of the transitions, i.e., edges, of the resulting two state signal. As described above, when used for many applications, including, but not limited to automotive applications, positions of the edges can be very important to proper operation of the automobile.

As described above, the magnetic field signal 52 can vary in amplitude due to a variety of environmental and electronic factors, for example, temperature and air gap between the magnetic field sensor and the sensed cam or gear. It would be desirable to maintain a threshold signal comparable to the calculated threshold 56 of FIG. 2 that is at a favorable position between positive peaks and negative peaks of the magnetic field signal 52, even as the amplitude of the positive and negative peaks changes, for example, due to temperature, air gap between the magnetic field sensing element 16 of FIG. 1 and the cam 26, or other parameters. With such an arrangement, edges of the resulting two state signal 72 can remain at the same positions even if the amplitudes of the positive and negative peaks of the magnetic field signal 52 change and even if they change asymmetrically.

Referring to FIG. 4, a magnetic field sensor 400 includes a Hall Effect element 402 driven by a current source 404. The Hall effect element 402 is responsive to a magnetic field as may be generated, for example, by a magnet 403 disposed proximate to or within the magnetic field sensor 400. Rotation of a gear 450 can result in variations of the magnetic field sensed by the Hall Effect element, further resulting in a magnetic field signal 402 a being an AC signal when the gear 450 rotates.

While a Hall effect element is shown, any type of magnetic field sensing element can be used. Also, while one magnetic field sensing element is shown, in other embodiments, there can be more than one magnetic field sensing elements coupled, for example, in a differential arrangement.

The magnetic field sensor 400 includes a signal path (analog or digital or mixed) comprised of an amplifier 408, a filter 410, which can be a programmable filter, a summing circuit 412, and an amplifier 414. The Hall Effect element 402 is configured to generate the magnetic field signal 402 a responsive to the magnetic field. The amplifier 408 (e.g., a gain adjustable analog circuit) is coupled to receive the magnetic field signal 402 a and to receive a gain control signal 416 a and configured to generate a gain adjusted signal 408 a. The filter 410 is coupled to receive the gain adjusted signal 408 a and configured to generate a filtered signal 410 a. The summing circuit 412 (e.g., an offset adjustable analog circuit) is coupled to receive the filtered signal 410 a and to receive an offset control signal 418 a and configured to generate an offset adjusted signal 412 a. The amplifier 414 is coupled to receive the offset adjusted signal 412 a and configured to generate an output signal 414 a having gain and offset correction.

It should be recognized that the output signal 414 a has an amplitude when the magnetic field sensor 402 is in the presence of a rotating gear 450 (or other moving ferromagnetic or magnetic object). The output signal 414 a can also have a residual offset.

It should also be recognized that the order of the circuit functions embodied by the amplifiers 408, 414 can be made in any order without changing the general functions described herein. It should also be recognized that the circuit functions can be made in either the analog or digital domains.

In some other embodiments, the offset temperature compensation is not performed, in which case, the temperature sensor 420 and the ADC 422 are not required, and the offset temperature correction coefficients need not be stored in the EEPROM 442.

In some other embodiments, the gain temperature compensation is not performed, in which case, the temperature sensor 420 and the ADC 422 are not required, and the gain temperature correction coefficients need not be stored in the EEPROM 442.

In some other embodiments, neither the gain temperature compensation nor the offset temperature compensation are performed, in which case, at least the segment processor 424, the coefficient table EEPROM 442, the temperature sensor, and the ADC 422 are not required. For these embodiments, the signal 414 a is an intermediate signal having no temperature compensation.

The magnetic field sensor 400 also includes a rotation module 417 coupled to receive the output signal 414 a and configured to generate a rotation output signal indicative of at least the rotation of the gear 450, but optionally also a speed of rotation of the gear 450, and optionally also a direction of rotation of the gear 450. The rotation module 417 is described below in conjunction with FIG. 6. Let it suffice here to say that the rotation module includes a comparator detector (e.g., a TPOS detector) and at least portions of a precision rotation detector.

The magnetic field sensor 400 also includes a temperature sensor 420, preferably disposed on the same substrate as other circuits of the magnetic field sensor 400. The temperature sensor 420 is configured to generate a temperature signal 420 a representative of a temperature experienced by the temperature sensor 420. An analog-to-digital converter (ADC) 422 is coupled to receive the temperature signal 420 a and configured to generate a digital temperature signal 422 a representative of the temperature signal 420 a.

The magnetic field sensor 400 can include a segment processor 424 coupled to receive the digital temperature signal 422 a. It will become apparent from discussion below that the segment processor 424 is configured to perform several functions. The segment processor 424 is configured to identify a temperature segment in which the digital temperature signal 422 a, (i.e. the temperature signal 420 a) falls. The segment processor 424 can also be coupled to receive a pair of gain correction coefficients 442 a and/or a pair of offset correction coefficients 442 b associated with the identified temperature segment. The pair of gain correction coefficients 442 a and/or pair of offset correction coefficients 442 b are associated with temperatures that bound the identified temperature segment. The pair of gain correction coefficients 442 a and/or pair of offset correction coefficients 442 b can be requested by the segment processor 424 via a control signal 426 c.

The segment processor 424 can be configured to interpolate between the pair of gain correction coefficients 442 a in accordance with the digital temperature signal 422 a to generate a sensor gain correction value 430 a. The gain control signal 416 a can be an analog signal related to and determined by the sensor gain correction value 430 a.

The segment processor 424 can also be configured to interpolate between the pair of offset correction coefficients 442 b in accordance with the digital temperature signal 422 a to generate a sensor offset correction value 432 a. The offset control signal 418 a can be an analog signal related to and determined by the sensor offset correction value 432 a.

It will be understood that the segment processor 424 can be a digital circuit that process digital signals or values. The segment processor 424 controls gain and/or offset of the analog circuits described above.

The magnetic field sensor 400 can include an EEPROM 442 configured to hold a plurality of gain correction coefficients and/or a plurality of offset correction coefficients, the coefficients associated with temperature boundaries of a plurality of temperature segments. In some embodiments, there are five selected temperature boundaries, each associated with a respective gain correction coefficient (TDSense) and a respective offset correction coefficient (DQVO).

The plurality of gain correction coefficients and the plurality of offset correction coefficients can be stored in the EEPROM 442 at the time of manufacture of the magnetic field sensor 400, or at any time thereafter, via a signal 438 a upon a communication link 438, which can be a serial communication link. A method of establishing the plurality of gain correction coefficients and the plurality of offset correction coefficients is described below in conjunction with FIG. 7.

The magnetic field sensor 400 can also include a user gain correction EEPROM 444 coupled to provide a user gain correction value 444 a to the segment processor 424. The magnetic field sensor 400 can also include a user offset EEPROM 446 coupled to provide a user offset correction value 446 a to the segment processor 424. The user gain EEPROM 444 can receive the user gain correction value 444 a via a signal 438 c upon the communication link 438. The user offset EEPROM 446 can receive the user offset correction value 446 a via a signal 438 d upon the communication link 438.

The magnetic field sensor 400 can also include a program control EEPROM 440 coupled to provide an interpolation control signal 440 a to the segment processor 424. Interpolation control is described more fully below. The program control EEPROM 440 can receive the interpolation control signal 440 a via a signal 438 b upon the communication link 438.

The segment processor 424 can include an interpolation processor 426 coupled to receive the digital temperature signal 422 a and coupled to receive the pair of gain correction coefficients 442 a and/or the pair of offset correction coefficients 442 b. In some embodiments, the interpolation processor 426 can also be coupled to receive the control signal 440 a. The control signal 440 a can determine a type of gain and/or offset interpolation to be performed by the interpolation processor 426. Types of interpolation are further described below.

The interpolation processor 426 is configured to generate an interpolated gain correction value 426 a and/or an interpolated offset correction value 426 b. To this end, the interpolation processor 426 is configured to identify the above-described temperature segment in which the digital temperature signal 422 a, (i.e. the temperature signal 420 a) falls. The interpolation processor 426 is also coupled to receive the above-described pair of gain correction coefficients 442 a and/or the above-described pair of offset correction coefficients 442 b associated with two temperatures that bound the identified temperature segment.

The interpolation processor 426 can use the digital temperature signal 422 a to identify in which one of the plurality of temperature segments the measured temperature lies. Accordingly, the proper pair of gain correction coefficients 442 a and/or the pair of offset correction coefficients 442 b can be requested by the interpolation processor 426 by the control signal 426 c.

The magnetic field sensor 400 can include a combining processor 428 coupled to receive the interpolated gain correction value 426 a and/or the interpolated offset correction value 426 b and coupled to receive the user gain correction value 444 a and/or the user offset correction value 446 a. The combining processor 428 is configured to combine the interpolated gain correction value 426 a with the user gain correction value 444 a and/or to combine the interpolated offset correction value 426 b with the user offset correction value 446 a. Accordingly, the combining processor 428 is configured to generate a combined gain correction value 428 a and/or a combined offset correction value 428 b, which can be stored in a gain adjust register 430 and an offset adjust register 432, respectively.

A digital-to-analog converter (DAC) 434 can be coupled to receive the stored gain correction value 430 a and configured to generate a gain correction signal 434 a received by a gain adjust circuit 416 configured to generate the gain control signal 416 a accordingly. A DAC 436 can be coupled to receive the stored offset correction value 432 a and configured to generate an offset correction signal 436 a received by an offset adjust circuit 418 configured to generate the offset control signal 418 a accordingly.

While the DACS 434, 436 are shown here, for embodiments described above in which various circuit functions are made in the digital domain, the DACS 434, 436 can be eliminated.

In one particular embodiment, the gain interpolation performed by the interpolation processor 426 to achieve the interpolated gain correction value 426 a is a linear interpolation of the form:

$\begin{matrix} {{SNS}_{OUT} = {{\frac{{CoeffB} - {CoeffA}}{32}*{{temp}\left\lbrack {4\text{:}0} \right\rbrack}} + {CoeffA}}} & (1) \end{matrix}$ where: CoeffA and CoeffB are the pair of gain correction coefficients 442 a bounding the identified temperature segment; and

-   -   temp[4:0] represents the five least significant bits of the         digital temperature signal 422 a, which can be a seven bit         value.

In some embodiments, the interpolation processor 426 holds a plurality of gain (sensitivity) processing options and the processing option (the interpolation type, i.e., the equation above) is selected in accordance with the control signal 440 a.

Some types of interpolation, e.g., higher order interpolations, may use more than two correction coefficients, and therefore, some embodiments store and use more than two gain and/or offset correction coefficients associated with each temperature segment.

In some embodiments, the combining processor 428 combines the interpolated gain correction value 426 a with the user gain correction value 444 a according to an equation below to, resulting in the combined gain correction value 428 a:

$\begin{matrix} {{SNS}_{OUT} = {\left\lbrack {\left\lbrack {{\frac{{CoeffB} - {CoeffA}}{32}*{{temp}\left\lbrack {4\text{:}0} \right\rbrack}} + {CoeffA}} \right\rbrack*\left( {{SENS}_{FINE} + K_{DEV}} \right)} \right\rbrack - K_{DEV}}} & (2) \end{matrix}$ where: SENS_(FINE) is the user gain correction value 444 a; and

-   -   K_(DEV) is a device specific constant representative of a         sensitivity of the particular type of magnetic field sensor         (e.g., decimal 74 or decimal 206)

In one particular embodiment, the offset interpolation performed by the interpolation processor 426 to achieve the interpolated offset correction value 426 b is a linear interpolation of the form:

$\begin{matrix} {{QVO}_{OUT} = {{\frac{{CoeffB} - {CoeFFA}}{32}*{{temp}\left\lbrack {4\text{:}0} \right\rbrack}} + {CoeffA}}} & (3) \end{matrix}$ where: CoeffA and CoeffB are the pair of offset correction coefficients 442 b bounding the identified temperature segment; and

-   -   temp[4:0] represents the five least significant bits of the         digital temperature signal 442 a, which can be a seven bit         value.

As described above, in some embodiments, the interpolation processor 426 holds a plurality of offset processing options and the processing option (the interpolation type, i.e., the equation above) is selected in accordance with the control signal 440 a. In some embodiments the selection can select among the following linear interpolation types, each differing by a factor of two (a one bit shift).

$\begin{matrix} {{QVO}_{OUT} = \frac{{\frac{{CoeffB} - {CoeFFA}}{32}*{{temp}\left\lbrack {4\text{:}0} \right\rbrack}} + {CoeffA}}{2}} & (4) \\ {{QVO}_{OUT} = {{\frac{{CoeffB} - {CoeffA}}{32}*{{temp}\left\lbrack {4\text{:}0} \right\rbrack}} + {CoeffA}}} & \begin{pmatrix} {5,{same}} \\ {{as}\mspace{14mu} 3} \end{pmatrix} \\ {\left\lbrack {{\frac{{CoeffB} - {CoeffA}}{32}*{{temp}\left\lbrack {4\text{:}0} \right\rbrack}} + {CoeffA}} \right\rbrack*2} & (6) \end{matrix}$

In some embodiments, the combining processor 428 combines the interpolated offset correction value 426 b with the user offset correction value 446 a according to an equation below, resulting in the combined offset correction value 428 b:

$\begin{matrix} {{QVO}_{OUT} = {{\frac{{CoeffB} - {CoeFFA}}{32}*{{temp}\left\lbrack {4\text{:}0} \right\rbrack}} + {CoeffA} + {QVO}}} & (7) \end{matrix}$ where: QVO is the user offset correction value 446 a.

It should be apparent from the above gain and offset equations that the user gain correction value 444 a is applied in a product and the user offset correction value 446 a is applied in a sum, as would be expected.

Referring now to FIG. 5, a graph 500 has a vertical axis 508 with a scale in units of sensitivity change in percent. A first horizontal axis 510 has a scale in units of temperature in degrees Celsius experienced by a magnetic field sensor (i.e., by the temperature sensor 420 of FIG. 4) and a second horizontal axis 512 has a scale in units corresponding to a seven bit digital code representative of temperature, but in decimal units from zero to one hundred twenty seven. The axis 512 corresponds to the digital temperature signal 422 a of FIG. 4.

A characteristic curve 502 is representative of a relative sensitivity (relative to sensitivity at room temperature 506) of a magnetic field sensor having no gain correction values applied. It can be seen that the relative sensitivity represented by the characteristic curve 502 tends to be lower at low and tends to be higher at high temperatures.

At a first temperature, −40 degrees Celsius, a gain correction coefficient 504 a (TDSense0 (FIG. 4)) is opposite from the relative sensitivity drop of the characteristic curve 502. It will be understood that the gain correction coefficient 504 a can be applied to the magnetic field sensor when the magnetic field sensor experiences the temperature of −40 degrees, resulting in essentially no sensitivity change from the sensitivity at room temperature 506. Similarly, other gain correction coefficients 504 b, 504 c, 504 d, 504 e (TDSense1, TDSense2, TDSense3, TDSense4, respectively (FIG. 4)) can be applied at other temperatures with which they are associated (11.25, 62.5, 113.75, 165.00 degrees Celsius, respectively) in order to provide no sensitivity change from the sensitivity at room temperature 506 at those particular temperatures.

Five temperature segments are shown, namely −40.00 to 11.25, 11.25 to 62.5, 62.5 to 113.75, and 113.75 to 165.00 degrees Celsius.

Within any temperature segment, e.g., the temperature segment 11.25 to 62.5, identified in accordance with an actual measured temperature experienced by the magnetic field sensor as represented by the digital temperature signal 422 a of FIG. 4, the interpolation processor 426 (FIG. 4) can interpolate between the gain correction coefficients (e.g., 504 b, 504 c) associated with boundaries of the identified temperature segment to establish an interpolated gain correction value (e.g., 426 a, FIG. 4) to be used at the particular measured temperature. The interpolated gain correction value can be applied to the magnetic field sensor 400 to keep the sensitivity of the magnetic field sensor essentially unchanged from the sensitivity at room temperature 506.

As shown and described above, the sensitivity interpolation can be a linear interpolation. However in other embodiments, the gain interpolation can be of another form, for example, a quadratic interpolation, or any other form of non-linear interpolation.

While five gain correction coefficients 504 a-504 e are shown and four associated temperature segments, in other embodiments, there can be more than five or fewer than five gain correction coefficients and more than four or fewer than four associated temperature segments. The number of gain correction coefficients and associated temperature segments can be selected according to a desired accuracy and according to a desired largest physical size of the EEPROM 442 (FIG. 4) that stores the gain correction coefficients. In general, the greater the number of gain correction coefficients that are stored in the EEPROM 442, the more accurate will be the interpolated gain correction coefficients and the more accurate will be the corrected relative sensitivity of the magnetic field sensor.

While the temperature segments are shown to be equal in numbers of degrees, in other embodiments, the temperature segments can have an unequal number of degrees. For example, in some embodiments, temperature segments near to room temperature 506 can have a larger (or smaller) temperature span than temperature segments further from room temperature 106.

Each individual magnetic field sensor of a particular type can have different gain correction coefficients 504 a-504 e generated by a process more fully described below in conjunction with FIG. 7. However, in some embodiments, each one of a particular type of magnetic field sensor can have the same gain correction coefficients 504 a-504 e.

As further described below in conjunction with FIG. 7, some of (or all of) the gain correction coefficients 504 a-504 e can be selected (i.e., measured) during production of the magnetic field sensor (or thereafter) by direct measurements of relative sensitivity at the plurality of temperatures of the specific one of the magnetic field sensors in which the specific gain correction coefficients 504 a-504 e are stored. However in some embodiments, fewer than all of the gain correction coefficients 504 a-504 e result from direct measurements and other ones of the gain correction coefficients 504 a-504 e are derived from the shape of the sensitivity characteristic curve 502. In other words, for example, the gain correction coefficient 504 a can be generated by a relative sensitivity measurement at −40.00 degrees and at room temperature 506, and other ones of the gain correction coefficients 504 b-504 e can be deduced by knowledge of a shape of the sensitivity characteristic curve 502.

The characteristic curve 502 as shown can be representative of an average sensitivity characteristic taken from a plurality of the same type of magnetic field sensor. Other types of magnetic field sensors can have characteristic curves with other shapes.

In using the characteristic curve 502 to derive some (or all) of the gain correction coefficients 504 a-504 e for a particular magnetic field sensor, it should be understood that the characteristic curve 502 can keep the same shape common to all of the same type of magnetic field sensors, but can be scaled up or down in magnitude for each individual magnetic field sensor of the same type. For example, if the relative sensitivity of an individual magnetic field sensor is measured at room temperature and also at −40 degrees, and if the relative sensitivity at −40 degrees is lower than that represented by the characteristic curve 502, it can be presumed that the characteristic curve of the magnetic field sensor being measured curves more downward at −40 degrees and more upward at 165 degrees, but otherwise maintains the same shape. Thus, by making only a room temperature sensitivity measurement and also a relative sensitivity measurement at any other temperature (relative to sensitivity at room temperature), a characteristic curve similar to (same shape as) the characteristic curve 502 (but with different scaling) can be derived and the other gain correction coefficients can be deduced.

It will be understood that the particular shape of the sensitivity characteristic curve 502 depends upon the particular type magnetic field sensor. Furthermore, the characteristic curve 502 can be slightly different (scaling) for different specific ones of the particular type of magnetic field sensor. Therefore, it may be advantageous to characterize a plurality of different specific ones of the particular type of magnetic field sensor, and take an average in order to identify the shape of the characteristic curve 502, which can thereafter be scaled up or down to suit each individual magnetic field sensor of the same type.

Referring now to FIG. 6, a graph 600 has a vertical axis 608 with a scale in units of DC offset voltage change in linear units represented by a nine bit digital value. A first horizontal axis 610 has a scale in units of temperature in degrees Celsius experienced by a magnetic field sensor (i.e., by the temperature sensor 420 of FIG. 4) and a second horizontal axis 612 has a scale in units corresponding to a seven bit digital code representative of temperature, but in decimal units from zero to one hundred twenty seven. The axis 612 corresponds to the digital temperature signal 422 a of FIG. 4.

A characteristic curve 602 is representative of a relative offset (relative to offset at room temperature 606) of a magnetic field sensor having no offset correction values applied. It can be seen that the offset represented by the characteristic curve 602 tends to be in one direction at low temperatures relative to the offset (nominally 0.0V) at room temperature and tends to be in the other direction at high temperatures relative to the offset at room temperature.

At a first temperature, −40 degrees Celsius, an offset correction coefficient 604 a (DQVO_0 (FIG. 4)) is opposite from the relative offset drop of the characteristic curve 602. It will be understood that the offset correction coefficient 604 a can be applied to the magnetic field sensor when the magnetic field sensor experiences the temperature of −40 degrees, resulting in essentially no offset change from the offset (0.0V) at room temperature 606. Similarly, other offset correction coefficients 604 b, 604 c, 604 d, 604 e (DQVO_1, DQVO_2, DQVO_3, DQVO_4, respectively (FIG. 4)) can be applied at other temperatures with which they are associated (11.25, 62.5, 113.75, 165.00 degrees Celsius, respectively) in order to provide no offset change from the offset at room temperature 606 at those particular temperatures.

As in FIG. 5, five temperature segments are shown, namely −40.00 to 11.25, 11.25 to 62.5, 62,5 to 113.75, and 113.75 to 165.00 degrees Celsius.

Within any temperature segment, e.g., the temperature segment 11.25 to 62.5, identified in accordance with an actual measured temperature experienced by the magnetic field sensor as represented by the digital temperature signal 422 a of FIG. 4, the interpolation processor 426 (FIG. 4) can interpolate between the offset correction coefficients (e.g., 604 b, 604 c) associated with boundaries of the temperature segment to establish an interpolated offset correction value (e.g., 426 b, FIG. 4) to be used at the particular measured temperature. The interpolated offset correction value can be applied to the magnetic field sensor to keep the offset of the magnetic field sensor essentially unchanged from the offset at room temperature 606.

As shown and described above, the offset interpolation can be a linear interpolation. However in other embodiments, the offset interpolation can be of another form, for example, a quadratic interpolation, or any other form of non-linear interpolation.

While five offset correction coefficients 604 a-604 e are shown and four associated temperature segments, in other embodiments, there can be more than five or fewer than five offset correction coefficients and more than four or fewer than four associated temperature segments. The number of offset correction coefficients and associated temperature segments can be selected according to a desired offset accuracy and according to a desired largest physical size of the EEPROM 442 (FIG. 4) that stores the offset correction coefficients. In general, the greater the number of offset correction coefficients that are stored in the EEPROM 442, the more accurate will be the interpolated offset correction coefficients and the more accurate will be the corrected relative offset of the magnetic field sensor.

While the temperature segments are shown to be equal in numbers of degrees, in other embodiments, the temperature segments can have an unequal number of degrees. For example, in some embodiments, temperature segments near to room temperature 606 can have a larger (or smaller) temperature span than temperature segments further from room temperature 606.

Each individual magnetic field sensor of a particular type can have different offset correction coefficients 604 a-604 e generated by a process more fully described below in conjunction with FIG. 7. However, in some embodiments, each one of a particular type of magnetic field sensor can have the same offset correction coefficients 604 a-604 e.

As further described below in conjunction with FIG. 7, some of (or all of) the offset correction coefficients 604 a-604 e can be selected (i.e., measured) during production of the magnetic field sensor (or thereafter) by direct measurements of relative offset at the plurality of temperatures of the specific one of the magnetic field sensors in which the specific offset correction coefficients 604 a-604 e are stored. However in some embodiments, fewer than all of the offset correction coefficients 604 a-604 e result from direct measurements and other ones of the offset correction coefficients 604 a-604 e are derived from the offset characteristic curve 602. In other words, for example, the offset correction coefficient 604 a can be generated by a relative offset measurement at −40.00 degrees and at room temperature 606, and other ones of the offset correction coefficients 604 b-604 e can be deduced by knowledge of a shape of the offset characteristic curve 602.

The characteristic curve 602 as shown can be representative of an average offset characteristic taken from a plurality of the same type of magnetic field sensor. Other types of magnetic field sensors can have offset characteristic curves with other shapes.

In using the offset characteristic curve 602 to derive some (or all) of the offset correction coefficients 604 a-604 e for a particular magnetic field sensor, it should be understood that the offset characteristic curve 602 can keep the same shape common to all of the same type of magnetic field sensors, but can be scaled up or down in magnitude for each individual magnetic field sensor of the same type. For example, if the relative offset of an individual magnetic field sensor is measured at room temperature and also at −40 degrees, and if the relative offset at −40 degrees is lower than that represented by the characteristic curve 602, it can be presumed that the characteristic curve of the magnetic field sensor being measured curves more downward at −40 degrees and more upward at 165 degrees, but otherwise maintains the same shape. Thus, by making only a room temperature offset measurement and also a relative offset measurement at any other temperature (relative to offset at room temperature), a characteristic curve similar to (same shape as) the characteristic curve 602 (but with different scaling) can be derived and the other offset correction coefficients can be deduced.

It will be understood that the particular shape of the offset characteristic curve 602 depends upon the particular type magnetic field sensor. Furthermore, the characteristic curve 602 can be slightly different (e.g., different scaling) for different specific ones of the particular type of magnetic field sensor. Therefore, it may be advantageous to characterize a plurality of different specific ones of the particular type of magnetic field sensor, and take an average in order to identify the shape of the offset characteristic curve 602, which can thereafter be scaled up or down to suit each individual magnetic field sensor of the same type.

From the above examples of FIGS. 5 and 6, it can be seen that in one embodiment, there are five gain correction coefficients associated with five temperatures and, five offset correction coefficients associated with the same five temperatures. However, the gain correction coefficients and the offset correction coefficients need not be associated with the same temperatures. The EEPROM 442 of FIG. 4 is shown to store the exemplary five gain correction coefficients (TDSense0 to TDSense4) and the five exemplary offset correction coefficients (DQVO_0 to DQVO_4).

It should be appreciated that FIGS. 7, 10, and 15 below show flowcharts corresponding to the below contemplated techniques which would be implemented in the magnetic field sensor 400 (FIG. 4). Rectangular elements (typified by element 704 in FIG. 7), herein denoted “processing blocks,” represent computer software instructions or groups of instructions. Diamond shaped elements (typified by element 1004 in FIG. 10), herein denoted “decision blocks,” represent computer software instructions, or groups of instructions, which affect the execution of the computer software instructions represented by the processing blocks.

Alternatively, the processing and decision blocks represent steps performed by functionally equivalent circuits such as a digital signal processor circuit or an application specific integrated circuit (ASIC). The flow diagrams do not depict the syntax of any particular programming language. Rather, the flow diagrams illustrate the functional information one of ordinary skill in the art requires to fabricate circuits or to generate computer software to perform the processing required of the particular apparatus. It should be noted that many routine program elements, such as initialization of loops and variables and the use of temporary variables are not shown. It will be appreciated by those of ordinary skill in the art that unless otherwise indicated herein, the particular sequence of blocks described is illustrative only and can be varied without departing from the spirit of the invention. Thus, unless otherwise stated the blocks described below are unordered meaning that, when possible, the steps can be performed in any convenient or desirable order.

Referring now to FIG. 7, an exemplary method 700 begins at a set of blocks 702 that can be performed in a factory upon manufacture of the magnetic field sensor 10 of FIG. 1. At block 704, a set of calibration temperatures and associated temperature segments are selected. In the examples given above in conjunction with FIGS. 4-6, there can be five selected temperatures, e.g., −40.00, 11.25, 62.5, 113.75, and 165.00 degrees Celsius and four associated temperature segments bounded by adjacent pairs of the selected temperatures. However, as described above there can be more than five or fewer than five selected temperatures and more than four or fewer than four associated temperature segments, and the selected temperatures need not be evenly spaced.

At block 706, relative gains and relative offsets (relative to gain and offset at room temperature) can be measured either at all of the selected temperatures, or at a subset of the selected temperatures, for example, only at −40.00 degrees Celsius.

At block 708, based upon the relative sensitivity measurement(s), gain and offset correction coefficients are established for the temperature(s) at which measurements were taken. The gain and offset correction coefficients can be opposite from the measured relative sensitivity and relative offset deviations.

At block 710, other gain and offset correction coefficients can be established for the selected temperatures at which direct measurements of relative sensitivity and offset are not taken for the specific magnetic field sensor under consideration. As described above, the establishment of the other gain and offset correction coefficients can be made in accordance with generation of a sensitivity characteristic curve and/or an offset characteristic curve, using knowledge of the shape of the curves as derived from an average of measurements of a plurality of magnetic field sensors of the same type. Using the same shape, the sensitivity (gain) characteristic curve and the offset characteristic curve can have the same shape as the average of the measurements, but can be scaled up or down in magnitude according to the sensitivity and offset measurement(s) made block 706.

At block 712, the gain and offset correction coefficients (e.g., five gain correction coefficients and five offset correction coefficients) are stored within the magnetic field sensor, for example, within the EEPROM 442 of FIG. 4 via a serial communication link, for example, the communication link 438 of FIG. 4.

At block 714, in some embodiments, a gain interpolation equation and/or an offset interpolation type (equation) can be selected from among a plurality of interpolation types. See equations 1, 3, 4, and 5 above.

At block 716, the selection of the interpolation types can be saved as a value, for example, in the EEPROM 440 of FIG. 4 via the serial communication link, for example, the communication link 438 of FIG. 4.

The remaining blocks of the process 700 can be performed by the magnetic field sensor when in the field in normal operation, either continuously or from time to time.

At block 718, the magnetic field sensor measures its temperature, for example, via the temperature sensor 420 of FIG. 4.

At block 720, the magnetic field sensor identifies in which one of the temperature segments selected at block 704 the measured temperature resides.

At block 722, the magnetic field sensor, for example, the interpolation processor 426 of FIG. 4, interpolates, in accordance with the measured temperature, between gain correction coefficients stored at block 712 that bound the identified temperature segment. An interpolated gain correction value (e.g., 426 a of FIG. 4) is thus established. The interpolation can be in accordance with equation 1 above.

At block 724 or earlier, the magnetic field sensor can receive a user gain correction value, for example the value 444 a stored in the user gain correction value EEPROM 444 of FIG. 4 via the communication link 438 of FIG. 4. In some embodiments, the user gain correction value is used to merely adjust a sensitivity of the magnetic field sensor between factors of 0.75 and 1.25 according to user preference.

At block 726, the interpolated gain correction value is combined with the user gain correction value (e.g., by the combining processor 428 of FIG. 4) to establish a combined gain correction value (e.g., 428 a of FIG. 4). At block 728, the combined gain correction value is stored, for example, in the gain adjust register 430 of FIG. 4. At block 730 the saved gain correction value is applied to the magnetic field sensor to adjust its sensitivity (i.e., gain) via the DAC 434 and the gain adjust circuit 416 of FIG. 4.

At block 732, the magnetic field sensor, for example, the interpolation processor 426 of FIG. 4, interpolates, in accordance with the measured temperature, between offset correction coefficients stored at block 712 that bound the identified temperature segment. An interpolated offset correction value (e.g., 426 b of FIG. 4) is thus established. The interpolation can be in accordance with equation 3 above.

At block 734 or earlier, the magnetic field sensor can receive a user offset correction value, for example the value 446 a stored in the user offset correction value EEPROM 446 of FIG. 4 via the communication link 438 of FIG. 4. At block 736, the interpolated offset correction value is combined with the user offset correction value (e.g., by the combining processor 426 of FIG. 4) to establish a combined offset correction value (e.g., 428 b of FIG. 4).

At block 738, the combined offset correction value is stored, for example, in the offset adjust register 432 of FIG. 4. At block 740, the saved offset correction value is applied to the magnetic field sensor to adjust its offset via the DAC 436 and the offset adjust circuit 418 of FIG. 4.

With the above-described technique, the magnetic field sensor can maintain a sensitivity and an offset that do not change or that change very little with respect to temperature of the magnetic field sensor compared to the sensitivity and offset of the magnetic field sensor at room temperature.

Because the sensitivity and the offset have been stabilized with respect to temperature by the above-described circuits and techniques, it will be appreciated that thresholds described below, which are derived from the signal 414 a of FIG. 4 by the rotation module 417 of FIG. 4 are also stabilized with respect to temperature. However, it should also be understood that, an air gap between the magnetic field sensor 402 and the gear 450 of FIG. 4 can be different from installation to installation, or can change with time, for example, due to mechanical wear or the like. Therefore, the magnitude of the signal 414 a can still change with respect to air gap dimensions, and thresholds described below, which are derived from the signal 414 a can still change or be different due to air gap changes or differences.

Referring now to FIG. 8, a rotation module 800 can be the same as or similar to the rotation module 417 of FIG. 4. The rotation module 800 is coupled to receive a signal 818, which can be the same as or similar to the signal 414 a of FIG. 4. As described above, a magnitude of the signal 414, and of the signal 818, are stabilized with respect to temperature, but can change with respect to mechanical considerations, for example, air gap.

The rotation module 800 can include two different types of rotation detectors, for example, a comparator detector 802 and a precision rotation detector 810. It will be understood that the comparator detector 802, in some embodiments, can operate as a true power on state (TPOS) detector. In particular, typically where one magnetic field sensor is used as shown above in conjunction with FIG. 4, the comparator detector 802 is operable as a tooth detector (as opposed to an edge detector), and therefore, provides a TPOS function, able to distinguish a tooth in the gear 450 (FIG. 4) from a valley, even when the gear 450 is not rotating.

However, in other embodiments, a magnetic field sensor similar to the magnetic field sensor 400 of FIG. 4 can use two or more magnetic field sensing elements coupled in a differential arrangement. These embodiments provide an edge detector (as opposed to a tooth detector), not capable of distinguishing a tooth from a valley when the gear 450 is not rotating, and therefore, do not provide a TPOS function. For these embodiments, the comparator detector 802 is not a TPOS detector, but can still be of the form shown and described herein.

In view of the above, it will be understood that the comparator detector 802 can be operable as a tooth detector (E.g., a TPOS detector) or as an edge detector, depending upon the arrangement of magnetic field sensing element(s) (e.g., 402, FIG. 4). Therefore, as used herein, the term “comparator detector” is used to describe and circuit detector that includes a comparator operable to receive a comparator threshold, and to compare a signal with the comparator threshold.

The comparator detector 802 essentially has a rapid startup at which time it provides an accurate comparator detector output signal 806 a, while precision rotation detector 810 takes longer to start up and to provide an accurate precision rotation detector output signal 810 a.

Precision rotation detectors of a variety of types are known. Some precision rotation detectors internally provide a positive peak signal 810 b representative of amplitudes of positive peaks of the signal 818 and a negative peak signal 810 c representative of negative peaks of the signal 818. Between the peaks, positive peak signal 810 b and the negative peak signal 810 c can hold values representative of amplitudes of the peaks. Thus, in many conventional arrangements the positive peak signal 810 b and the negative peak signal 810 c have stepped type characteristics achieving and holding respective peaks of the input signal 818.

The comparator detector 802 can include a comparator 806, which can be either an analog comparator or a digital comparator. The comparator 806 is coupled to receive a comparator threshold 816 a (e.g., TPOS threshold) generated by a threshold module 816, described more fully below in conjunction with FIG. 9.

An output switch 812 can be coupled to receive the comparator detector output signal 806 a and the precision rotation detector output signal 810 a. By way of a control signal 808 a generated by a switch change logic module 808, the rotation module 800 generates as a rotation output signal 812 a representative of a selected one of the comparator detector output signal 806 a or the precision rotation detector output signal 810 a. The rotation output signal 812 a can be a two state output signal for which a high state is indicative of one of the teeth of the gear 450 of FIG. 4 being proximate to the magnetic field sensing element 402, and for which a low state is indicative of one of the valleys of the gear 450 being proximate to the magnetic field sensing element 402. However, in other embodiments, states of the rotation output signal 812 a can be reversed from those described above.

It will be appreciated that the rotation output signal 812 a can be representative of rotation of the gear 450, and also can be representative of speed of rotation of the gear 450. In some embodiments, the rotation output signal 812 a can also be representative of a direction of rotation of the gear 450. Magnetic field sensors, i.e., rotation detectors, that provide the rotation output signal 812 a that is also indicative of the direction of rotation are known Exemplary arrangements can be found in U.S. Pat. No. 6,815,944, issued Nov. 9, 2004, U.S. Pat. No. 7,026,808, issued Apr. 11, 2006, U.S. Pat. No. 7,772,838, issued Apr. 29, 2008, U.S. Pat. No. 7,592,801, issued Sep. 22, 2009, U.S. Pat. No. 7,622,914, issued Nov. 24, 2009, U.S. Pat. Nos. 7,772,838, and 7,253,614, issued Aug. 7, 2007, all of which patents are incorporated by reference herein in their entirety, and all of which patents are assigned to the assignee of the present invention.

The rotation output signal 812 a can be the same as or similar to the output signal 417 a of FIG. 4. In some embodiments, the rotation output signal 812 a is the only output signal from the magnetic field sensor 400 of FIG. 4.

In some embodiments, the rotation module 800 can include an output format module 814 coupled to receive the rotation signal 812 a and configured to provide a formatted rotation output signal 814 a. Like the rotation output signal 812 a, the formatted rotation output signal 814 a can also be indicative of at least one of a rotation, a speed of rotation, or a direction of rotation of the gear 450 of FIG. 4. The formatted rotation output signal 814 a can be provided in one of a variety of formats, for example, a SENT format, a CAN format, or an I2C format. Other formats are also possible.

In some other embodiments, the rotation module 800 does not include the switch change logic 808 or the output switch 812, and the comparator detector output signal 806 a is used as the rotation output signal from the rotation module 800 at all times. For these embodiments, the precision rotation detector output signal 810 a may not be generated. In other words, the precision rotation detector 810 can be used to generate only the positive and negative peak signals 810 b, 810 c, or only one of the positive or negative peak signals 810 b, 810 c.

Referring now to FIG. 9, a threshold module 900 can be the same as or similar to the threshold module 816 of FIG. 8. The threshold module 900 can include a measured threshold module 906 coupled to receive positive and negative peak signals 904 a, 904 b, respectively. The positive and negative peak signals 904 a, 904 b can be the same as or similar to the positive and negative peak signals 810 b, 810 c of FIG. 8, and can similarly be indicative of magnitudes of positive peaks (P+) and negative peaks (P−) of the temperature controlled signal 414 a of FIG. 4.

The measured threshold module 906 is configured to generate a measured threshold value 906 a. For reasons described above in conjunction with FIG. 4, the measured threshold value 906 a is stable with respect to temperature, but can still change, for example, in accordance with electrical noise, and/or in accordance with changes of the air gap between the gear 450 and the magnetic field sensing element 402 of FIG. 4.

As used herein, the term “signal” is used to describe an analog or digital voltage or current time waveform. As used herein, the term “value” is used to describe an amplitude and/or offset characteristic of an analog or digital signal at a point in time. As used herein, the term “value” is also used to describe a result of a calculation at a point in time involving the amplitude and/or offset characteristic of the analog or digital signal.

The measured threshold module 906 can calculate the measured threshold value 906 a as a combination of the positive and negative peak signals 904 a, 904 b. For example, the measured threshold value 906 a can be a value representative of a predetermined percentage, for example, seventy percent, of a voltage difference between the positive and negative peak signals 904 a, 904 b. A new measured threshold value 906 a can be calculated from time to time, or can be calculated when either one or both of the positive peak signal 904 a or the negative peak signal 904 b change in value.

In some other embodiments, the measured threshold module 906 is coupled to receive only one of the positive peak signal 904 a or the negative peak signals 904 b, in which case, the measured threshold value 906 a is calculated based only upon the received one of the signals.

For example, the measured threshold value 906 a can be a value representative of a predetermined percentage, for example, ten percent, of the positive peak signal 904 a.

The threshold module 900 can also include a memory device 908, which can be in nonvolatile memory device, for example, an EEPROM.

The memory device 908 can include a stored threshold memory region 910 coupled to receive and to store the measure threshold value 906 a. The measured threshold value 906 a can be stored in the memory device 908 at a plurality of storage times, but, in particular, at a storage time either at or immediately prior to a power down of the magnetic field sensor 400 of FIG. 4.

Storage and storage times are described more fully below.

A stored measured threshold value 910 a can be provided by the memory stored threshold memory region 910. In this way, upon powering up again, the magnetic field sensor 400 can use a stored measured threshold value 910 a in the comparator detector 802 of FIG. 8 immediately upon powering up.

A backup memory region 912 can store one or more backup values of the measured threshold value 906 a. The backup memory region 912 can store the measured threshold value 906 a at different times than the stored threshold memory region 910 stores the measured threshold value 906 a. With the backup arrangement, the threshold module 900 is able to reliably store the measured threshold value in either the backup memory region 912 or in the measured threshold memory region 910, avoiding at least one of the memory regions at a time when the magnetic field sensor 400 of FIG. 4 is powering down, during which time storage may be unreliable.

The memory device 908 can also include an initial threshold memory region 916 configured to store a predetermined initial threshold value, and configured to provide a stored predetermined initial threshold value 916 a. It should be understood that the magnetic field sensor 400 of FIG. 4 must-have a starting point for the comparator threshold 816 a of FIG. 8 the very first time that the magnetic field sensor 400 first powers up. The stored initial predetermined threshold value 916 a is used for this purpose.

The memory device 908 can also include a safety word storage area 914 configured to store a digital bit or digital word indicative of a time when storage is ongoing in the stored threshold memory region 910. The stored bit or word can be indicative of an ongoing storage into an indicated one of the stored threshold memory region 910 and the backup stored threshold region 912.

A threshold selection module 918 can be coupled to receive the initial threshold value 916 a, and at least one of the measured threshold value 906 a, the stored measured threshold value 910 a, or the stored backup measured threshold value 912 a. The threshold selection module 918 is configured to generate a comparator threshold signal 918 a as a selected one of the initial threshold value 916 a, the measured threshold value 906 a, the stored measured threshold value 910 a, or the stored backup measured threshold value 912 a.

A memory/threshold controller 920 is coupled to control the memory device 908 by way of a control line 920 a, controlling when storage of the measured threshold value 906 a occurs. The memory/threshold controller 920 can also provide a control line 920 c, which controls the selection of which one of the initial threshold value 916 a, the stored measured threshold value 910 a, or the stored backup measured threshold value 912 a is provided as the comparator threshold value 918 a.

The memory/threshold controller 920 can be coupled to receive one or more of a variety of signals, for example, the stored measured threshold value 910 a, the measured threshold value 906 a, a power on-off signal 922 representative of a power on or a power off of the magnetic field sensor 400 of FIG. 4, a comparator detector output signal 902, which can be the same as or similar to the comparator detector output signal 806 a of FIG. 8, or a precision rotation detector output signal 903, which can be the same as or similar to the precision rotation detector output signal 810 a of FIG. 8.

In operation, the memory/threshold controller 920 can use the various inputs signals in a variety of ways to control the storage of the measured threshold value 906 a into the memory device 908, and to control the threshold selection module 918.

With regard to storage of the measured threshold value 906 a into the memory device 908, in one embodiment, the memory/threshold controller can cause the storage only when the measured threshold value 906 a changes by a predetermined amount, which amount can be zero or more.

In another embodiment, the memory/threshold controller 920 can cause the storage only when the measured threshold value 906 a differs from the stored measured threshold value 910 a by a predetermined amount, which amount can be zero or more.

In another embodiment, the memory/threshold controller 920 can cause storage whenever the power on/off signal 922 first becomes indicative of the power off condition of the magnetic field sensor 400 of FIG. 4. For these embodiments, it is presumed that the magnetic field sensor 400 of FIG. 4 is coupled to some charge storage device, for example, a capacitor, such that the magnetic field sensor 400 does not instantaneously power off.

In another embodiment, the memory/threshold controller 920 can cause the storage only when the comparator detector output signal 902 has changed state by a predetermined number of times after the magnetic field sensor 400 of FIG. 4 has powered on. It will be understood that, these embodiments allow the precision rotation detector 810 of FIG. 8 to achieve a stable positive peak signal 810 b and a stable negative peak signal 810 c.

In another embodiment, the memory/threshold controller 920 can cause the storage when the previously stored threshold 816 a (FIG. 4) presently in use by the comparator detector 802 (FIG. 4) is likely to be incorrect as evidenced by a difference in switching rates of the comparator detector output signal 806 a (FIG. 4) and the precision rotation detector output signal 810 a (FIG. 4).

In another embodiment, the memory/threshold controller 920 can cause the storage only when the precision rotation detector output signal 903 has changed state by a predetermined number of times after the magnetic field sensor 400 of FIG. 4 has powered on. It will be understood that, these embodiments also allow the precision rotation detector 810 of FIG. 8 to achieve a stable positive peak signal 810 b and a stable negative peak signal 810 c.

Some types of precision rotation detectors are operable to detect peaks of the magnetic field signal, i.e., the magnetic field signal 414 a of FIG. 4, and to provide a precision rotation detector output signal with state transitions that occur upon occurrences, or near to occurrences, of positive peaks or negative peaks of the magnetic field signal. (see, e.g., above-mentioned U.S. Pat. No. 7,199,579, issued Apr. 2, 2007) Therefore, the above-described embodiment for which storage occurs only when the precision rotation detector output signal 903 has changed state by a predetermined number of times can, in some embodiments, be equivalent to storage occurring only when a predetermined number of peaks have occurred in the magnetic field signal.

Storage operation of the memory/threshold controller 922 described by exemplary embodiments above can also have any combination of the above storage arrangements.

In some embodiments, whenever a storage is ongoing by the memory/threshold controller 920 the memory/threshold controller 920 can store a safety word into the safety word storage area 914.

The threshold module 900 can also optionally include a diagnostic module 924, which can be coupled to receive one or more of the stored measured threshold value 910 a or the measured threshold value 906 a. The diagnostic module 924 can be configured to generate a pass fail signal or value 924 a. The pass fail value 924 a can be indicative of the stored measured threshold value 910 a and the measured threshold value 906 a differing by more than a predetermined amount, which may occur, for example, when the magnetic field sensor 400 of FIG. 4 is powered down for a period of time and then re-powered.

As described above, it should be appreciated that, at a first power up of the magnetic field sensor 400 of FIG. 4, the control signal 920 c can be used to direct the initial threshold value 916 a to be the comparator threshold value 918 a for some short time after the magnetic field sensor 400 is first powered up. Thereafter, the magnetic field sensor 400 can use either the stored measured threshold 910 a, the measured threshold 906 a, or the backup measured threshold 912 a as the comparator threshold 918 a, depending upon a condition of the word stored in the safety memory area 914 as detected by the memory/threshold controller 920.

With the above-described arrangement, it will be appreciated that the measured threshold value 906 a, and therefore, the stored measured threshold value 910 a, the stored backup measured threshold value 912 a, and the comparator threshold 918 a have already been gain and/or offset temperature compensated by operation of the circuits described above in conjunction with FIG. 4. However, as described above, the values can still change as the air gap between the gear 450 and the magnetic field sensor 402 of FIG. 4 changes or is different in different installations.

In some embodiments, optionally, the threshold module 900 can include a scaling module 926 and/or an offset module 928. The scaling module 926 is configured to apply a predetermined scaling, and the offset module is configured to apply a predetermined offset to the comparator threshold 918 a, providing an alternate comparator threshold 928 a suitable for use by some embodiments of the comparator detector 802 of FIG. 8. Of course the applied scaling can be one and the applied offset can be zero.

Furthermore, for embodiments described above in conjunction with FIG. 4, which do not have temperature compensation (no gain temperature compensation, and/or no offset temperature compensation, or neither) still the initial threshold value 916 a, the measured threshold value 906 a, the stored measured threshold value 910 a, or the stored backup measured threshold value 912 a can be selected for use as the comparator threshold value 918 a, essentially with no alteration of the values, or with minimal alteration of the values before they are used by the comparator detector 802 of FIG. 8. The minimal alteration can include, for example, the above-described predetermined scaling and/or the predetermined offset to provide the alternate comparator threshold 928 a suitable for use by some embodiments of the comparator detector 802 of FIG. 8. Of course the applied scaling can be one and the applied offset can be zero.

Referring now to FIG. 10, a process 1000 can be used in conjunction with the threshold module 900 of FIG. 9. The process 1000 begins at block 1002, where the magnetic field sensor 400 of FIG. 4 is powered on. At block 1004, it is decided whether the power on of the magnetic field sensor 400 is a very first power on.

If the power on is not the very first power on, then at block 1005, the safety word (i.e., stored in the safety memory area 914 of FIG. 9) is read. From the above discussion, it will be apparent that the status of the safety word stored in safety storage area 914 is indicative of a proper or improper storage of the measured threshold value 906 a in the stored threshold memory region 910, a proper or improper storage of the measured threshold value 906 a in the backup stored threshold memory region 912, or all of the above.

At block 1006, depending upon the status of the safety word read at block 1005, the stored measured threshold value 910 a (FIG. 9) or the stored backup measured threshold value 912 a is read from the memory device 908 of FIG. 9.

At block 1008, the stored measured threshold value 910 a, or the stored backup measured threshold value 912 a, is used as the comparator threshold value 918 a by the comparator detector 802 of FIG. 8.

At block 1010, if necessary, a wait time can be performed while the precision rotation detector 810 of FIG. 8 provides stable positive and negative peak values 810 b, 810 c (FIG. 8).

At block 1012, it is determined whether a predetermined condition is met. The predetermined conditions are described above in conjunction with FIG. 9. For example, one predetermined condition is that a predetermined number of transitions of the comparator detector output signal 902 of FIG. 9 has occurred. Other predetermined conditions are described above, and can be used in any combination.

If the condition or conditions have been met, then the process 1000 proceeds to a set of blocks 1014-1032, where the measure threshold value 906 a of FIG. 9 is written into both the stored threshold memory region 910 and into the backup stored threshold region 912.

At block 1014, a value is written into the safety storage area 914 of FIG. 9 to indicate that storage is ongoing into the stored threshold memory region 910. At block 1016, the measured threshold value 906 a is written into the stored threshold memory region 910.

At block 1018, the word written into the safety word storage area 914 is changed to indicate that proper storage was made into the stored threshold memory region 910 and that storage into the backup stored threshold region 912 is ongoing.

At block 1020, the measured threshold value 906 a is written into the backup stored threshold memory region 912. At block 1032 the word stored in the safety memory region 914 is again changed to indicate that proper storage has occurred in both the stored threshold memory region 910 and in the backup stored threshold memory region 912.

At block 1034, the stored safety word in the safety memory region 914 is read, for example by the memory/threshold controller 920. At block 1036, depending on the value of the safety word read at block 1034, either the stored measured threshold value 910 a or the stored backup measured threshold value 912 a is read from the memory device 908.

At block 1038, the stored measured threshold value 910 a or the stored backup measured threshold value 912 a read at block 1036 is used as the comparator threshold value 918 a of FIG. 9, i.e., by the comparator detector 802 of FIG. 8. However, in some other embodiments, the comparator threshold value 918 a of FIG. 9 (used at block 1038) can instead correspond to the measured threshold value 906 a of FIG. 9 other than at times near to a power up (block 1002) of the magnetic field sensor 400 of FIG. 4, i.e., at times after the threshold learning of block 1010 has stabilized. For these embodiments, the reading of blocks 1034 and 1036 can be omitted.

At block 1012, if the predetermined condition is not met, then the process 1000 loops at block 1012 until such time that the predetermined condition is met. At block 1004, if the power on is the very first power on then the process at block 1018 uses the initial threshold value stored in the initial threshold region 916 of FIG. 9 as the comparator threshold 918 a of FIG. 9. Then the process jumps to block 1010.

It will be understood that a power down of the magnetic field sensor 400 of FIG. 4 that uses the process 1000 can occur at any time during the process 1000. Such power down will not be harmful. In particular, with the above arrangement that uses the safety word within blocks 1014-1032, at all times at least one of the stored measured threshold value 910 a or the stored backup measured threshold value 912 a will have been properly stored, and, by way of the safety word stored in the safety memory region 914, an acceptable one of the stored values can be used.

Referring now to FIG. 11, a graph 1100 can be the same as or similar to the graph 50 of FIG. 2. Here, however, are shown positive peak values 1108 a, 1108 b, 1108 c, 1108 d of a signal 1102, and negative peak values 1110 a, 1110 b, 1110 c, 1110 d of the signal 1102. The positive peak values 1108 a, 1108 b, 1108 c, 1108 d are representative of values of the positive peak signal 904 a of FIG. 9, and the negative peak values 1110 a, 1110 b, 1110 c, 1110 d are representative of values of the negative peak signal 904 b of FIG. 9. It will be understood that the signal 1102 is representative of one full rotation of the gear 450 of FIG. 4, therefore having four peaks and four valleys.

As described above in conjunction with FIG. 9, the measured threshold module 906 can combine the positive peak signal 904 a and the negative peak signal 904 b in a variety of ways. In one embodiment, the measured threshold module 906 can identify a smallest one of the positive peak values associated with one full rotation of the gear 450, e.g., 1108 c, and a largest one of the negative peak values associated with the same full one rotation of the gear 450, e.g., 1110 d. The measured threshold module 906 can use the two identified values and can set the measured threshold value 906 a according to a predetermined percentage of a difference between the two values.

In another embodiment, the measured threshold module 906 of FIG. 9 can compute four different threshold values, a first threshold value according to a predetermined percentage of a difference between the positive peak value 1108 a and the negative peak value 1110 a, a second threshold value according to a predetermined percentage of a difference between the positive peak value 1108 b and the negative peak value 1110 b, a third threshold value according to a predetermined percentage of a difference between the positive peak value 1108 c and the negative peak value 1110 c, and a fourth threshold value according to a predetermined percentage of a difference between the positive peak value 1108 d and the negative peak value 1110 d. The measured threshold module 906 can average the four threshold values to generate the measured threshold value 906 a. In another embodiment, the measured threshold module 906 can select a largest one of the four threshold values. In another embodiment, the measured threshold module 906 can select a smallest one of the four threshold values.

In another embodiments, the measured threshold module 906 of FIG. 9 can provide as the measured threshold value 906 a (FIG. 9), a selected one of the positive peak values 1108 a-1108 d, a selected one of the negative peak values 1110 a-1110 d, an average of the positive peak values 1108 a-1108 d, an average of the negative peak values, a largest one of the positive peak values 1108 a-1108 d, a smallest one of the positive peak values 1108 a-1108 d, a largest one of the negative peak values 1110 a-1110 d, or a smallest one of the negative peak values 1110 a-1110 d.

Other combinations of the values 1108 a-1108 d of the positive peak signal and the values 1110 a, 1110 d of the negative peak signal can also be used. In still other arrangements, more positive peak values and/or more negative peak values, due, for example, to more gear teeth, or due to more revolutions of the gear 450 of FIG. 4, can be used in combined in ways similar to those ways described above. In still other embodiments, an offset value can be added or subtracted to any one of the above-mentioned values to achieve the measured threshold value that is stored.

In general, the measured threshold module 906 of FIG. 9 can be configured to select at least one of a largest positive peak value from among the plurality of values of the positive peak signal (904 a, FIG. 9), a smallest positive peak value from among the plurality of values of the positive peak signal 904 a, a largest negative peak value from among the plurality of values of the negative peak signal (904 b, FIG. 9), or a smallest negative peak value from among the plurality of values of the negative peak signal 904 b, and configured to generate the measured threshold value 906 a in accordance with the at least one selected value.

Though the signal 1102 is shown to have positive peaks that are roughly the same and negative peaks that are roughly the same, for other gears, other than the gear 450 of FIG. 4, and, in particular, for gears that have very narrow teeth or very narrow valleys, positive peaks and/or negative peaks of the signal generated by rotation of the gear can have values that differ from other ones of the positive peaks and/or negative peaks. The above arrangements tend to provide an ultimate comparator threshold 1106 through which all the positive to negative and negative to positive transitions of the signal 1102 pass.

Referring to FIG. 12, a magnetic field sensor 1200 includes a plurality of magnetic field sensing elements 1202 a-1202 c. The magnetic field sensing elements 1202 a-1202 c may take various forms such as Hall effect elements of various types as illustrated, magnetoresistance elements of various types, or a combination thereof.

The sensing elements 1202 a-1202 c are responsive to a magnetic field as may be generated, for example, by a magnet 1203 disposed proximate to or within the magnetic field sensor package. Rotation of a target 1224, such as a gear with gear teeth or ring magnet with segments of alternating magnetic polarities, can result in variations of the magnetic field sensed by the sensing element 1202 a-1202 c.

Each sensing element 1202 a-1202 c generates a respective differential magnetic field signal coupled to inputs of one or more amplifiers 1208 a, 1208 b, as shown. More particularly, the differential magnetic field signals generated by elements 1202 a and 1202 b are coupled to amplifier 1208 a, which amplifier generates a differential magnetic field signal 1210 a. Similarly, the differential magnetic field signals generated by elements 1202 b and 1202 c are coupled to amplifier 1208 b, which amplifier generates a differential magnetic field signal 1210 b. With this arrangement, differential magnetic field signal 1210 a is representative of the difference between the magnetic field signals generated by elements 1202 a and 1202 b and differential magnetic field signal 1210 b is representative of the difference between the magnetic field signals generated by elements 1202 b and 1202 c. Differential magnetic field sensing in this manner can be advantageous to reject stray fields. This is because, since all of the elements 1202 a-1202 c generally experience the same stray fields, taking the difference between signals sensed by two elements will tend to cancel effects of the stray field.

Analog-to-digital converters (ADCs) 1212 a, 1212 b convert differential magnetic field signals 1210 a, 1210 b into respective digital signals 1214 a, 1214 b for further processing. A digital controller 1218 is coupled to receive and process the digital signals 1214 a, 1214 b to generate controller output signals 1220 a, 1220 b. More particularly, output signals 1220 a, 1220 b can be coupled to driver circuits 1226 a, 1226 b, such as the illustrated open drain driver configurations, to thereby generate respective sensor output signals 1228 a, 1228 b. As will be described, sensor output signals 1228 a, 1228 b can be representative of various aspects of the target 1224, including but not limited to speed of rotation, direction of rotation, angular and/or rotational position. The digital controller 1218 is described further below in connection with FIGS. 13-15.

Sensor 1200 can be considered to include two so-called “channels” comprised of processing circuitry dedicated to processing magnetic field signals from one or more respective sensing elements 1202 a-1202 c. For example, a first, or right channel can include amplifier 1208 a, ADC 1212 a, a portion of controller 1218, and output driver 1226 a and can be configured to process magnetic field signals generated by sensing elements 1202 a, 1202 b to provide sensor output signal 1228 a, as shown. Similarly, a second, or left channel can include amplifier 1208 b, ADC 1212 b, a portion of controller 1218, and output driver 1226 b and can be configured to process magnetic field signals generated by sensing elements 1202 b, 1202 c to provide sensor output signal 1228 b, as shown. As will become apparent, the sensing elements associated with each channel have the same spatial relationship with respect to each other (e.g., such as the illustrated 1.75 mm spacing between sensing elements) and different respective spatial relationships with respect to the target 1224 as is useful in providing certain target information such as rotation direction. Designations of “right” and “left” are arbitrary. It will be appreciated that each channel can include less, more, or different processing circuitry than that shown in FIG. 12. It will also be appreciated that even in embodiments not implementing direction detection, it can be desirable to have multiple processing channels for reasons of redundancy, particularly in safety critical applications.

The magnetic field sensor 1200 also includes a temperature sensor 1240, that may be the same as or similar to the temperature sensor 420 of FIG. 4. An ADC 1242 can be coupled to receive an output signal from the temperature sensor 1240 and generate a digital temperature signal 1244 representative of the temperature experienced by the sensor 1200 for use by the controller 1218. Sensor 1200 can include additional elements and functionality shown in connection with FIG. 4, such as gain and/or offset compensation.

Sensor 1200 can have a terminal 1230 coupled to a power supply denoted as Vcc and a terminal 1232 coupled to a reference voltage, for example, a ground voltage, denoted as GND. Output terminals 1234, 1236 permit communication of sensor output signals 1228 a, 1228 b to circuits and systems external to the sensor. Sensor 1200 can be provided in the form of an integrated circuit (IC), with terminals 1230, 1232, 1234, and 1236 provided by pins or leads of the IC.

Referring to FIG. 13, an example controller 1300 (as may provide controller 1218 of FIG. 12) is coupled to receive signals 1332 a, 1332 b, which can be the same as or similar to signals 1214 a, 1214 b of FIG. 12, respectively and thus, can be referred to generally as magnetic field signals or signals representative of a magnetic field. Controller 1300 can include two different types of detectors, for example, comparator detectors 1302 a, 1302 b and precision rotation detectors 1310 a, 1310 b. Furthermore, the controller 1300 can be arranged to provide two signal processing channels, one (including comparator detector 1302 a and precision detector 1310 a) for processing signal 1332 a and the other (including comparator detector 1302 b and precision detector 1310 b) for processing signal 1332 b, as shown.

Controller 1300 further includes switch channel logic 1308 a, 1308 b, output switches 1312 a, 1312 b, output format modules 1314 a, 1314 b, threshold modules 1316 a, 1316 b, and a direction detection module 1320. For simplicity, the operation of the controller 1300 is described in detail in connection with the processing channel including comparator detector 1302 a, precision detector 1310 a, threshold module 1316 a, switch logic 1308 a, output switch 1312 a, and output format module 1314 a. It should be appreciated that the processing channel including detector 1302 b, detector 1310 b, threshold module 1316 b, switch logic 1308 b, output switch 1312 b, and output format module 1314 b can operate in essentially the same manner.

The comparator detector 1302 a essentially has a rapid startup at which time it provides an accurate comparator detector output signal 1318 a, while precision detector 1310 a takes longer to provide an accurate precision rotation detector output signal 1324 a.

Comparator detector 1302 a can include a comparator 1306 a, which can be an analog comparator or a digital comparator. The comparator 1306 a is coupled to receive a comparator threshold 1326 a (e.g., an interpolated threshold) generated by threshold module 1316 a, described more fully below in conjunction with FIG. 14. Suffice it to say here that the interpolated threshold 1326 a (and likewise counterpart interpolated threshold 1326 b for the other processing channel) is based in part on at least two stored threshold values, each associated with a different temperature. To this end, a temperature signal 1346 that can be the same as or similar to temperature signal 1244 (FIG. 12) can be coupled to the threshold modules 1316 a, 1316 b.

Comparator 1306 a compares the comparator threshold 1326 a to a signal representative of a magnetic field signal, as may be provided by magnetic field signal 1332 a. The comparator detector output signal 1318 a can be a two state output signal for which transitions between a high state and a low state are indicative of edges of target features passing the sensor and thus, which output signal can provide an indication of target rotation speed.

Precision detector 1310 a can take various forms and provides a positive a positive peak signal 1328 a representative of amplitudes of positive peaks of the signal 1332 a and a negative peak signal 1330 a representative of negative peaks of the signal 1332 a. In an embodiment, precision detector 1310 a can include a comparator for comparing the magnetic field signal 1332 a to a precision threshold that is a predetermined percentage, for example, seventy percent, of a voltage difference between the positive and negative peak signals 1328 a, 1330 a. Like the comparator detector output signal 1318 a, the precision detector output signal 1324 a can be a two state output signal for which transitions between a high state and a low state are indicative of edges of target features passing the sensor and thus, which output signal can provide an indication of target rotation speed.

An output switch 1312 a can be coupled to receive the comparator detector output signal 1318 a and the precision detector output signal 1324 a. By way of a control signal 1322 a generated by a switch channel logic 1308 a, the controller 1300 generates an output signal 1340 a representative of a selected one of the comparator detector output signal 1318 a or the precision detector output signal 1324 a. For example, the output signal 1340 a can be provided by the comparator output signal 1318 a for a time period near to a start up of the magnetic field sensor and thereafter, can be provided by the precision detector output signal 1324 a. Various schemes are possible for generating control signal 1322 a. For example, the control signal 1322 a may cause the output signal to be provided by the precision detector signal 1324 a after the output signal 1324 a has changed state a predetermined number of times, as may correspond to a predetermined time after startup of the sensor and/or to a predetermined number of features of a target passing by the sensor. The control signal 1322 a can cause the precision detector output signal 1324 a to provide the output signal 1340 a at a time corresponding to an end of a calibration interval and can be based on other conditions such as the magnetic field signal 1332 a achieving a predetermined peak-to-peak voltage level. In embodiments, even after the calibration interval, the switch channel logic 1308 a can optionally cause the output signal 1340 a to be provided by the comparator detector output signal 1318 a.

Output format module 1314 a can be coupled to receive the output signal 1340 a and configured to provide a formatted output signal 1350 a. Formatted output signal 1350 a can be indicative of one or more of a rotation, a speed of rotation, or a direction of rotation of the target and can be provided in a variety of formats, including but not limited to a SENT format, a CAN format, or an I²C format. Formatted output signals 1350 a, 1350 b can be the same as or similar to the output signals 1220 a, 1220 b of FIG. 12.

In some embodiments, the switch channel logic 1308 a and/or the output switch 1312 a can be omitted and the comparator detector output signal 1318 a can used to generate the sensor output signal at all times. For these embodiments, the precision rotation detector output signal 1324 a may not be generated and the precision rotation detector 1310 a can be used to generate one or both of the positive and negative peak signals 1328 a, 1330 a.

Direction detection module 1320 is responsive to output signals 1340 a, 1340 b and is configured to determine a direction of rotation of the target. Various direction detection schemes are possible and an example is described below in connection with FIG. 16. Suffice it to say here that an output signal 1352 of the direction detection module 1320 can be coupled to the output format modules 1314 a, 1314 b for use in generating respective formatted sensor output signals 1350 a, 1350 b.

The configuration of FIGS. 12 and 13 with two processing channels, each processing a magnetic field signal based on spatially separated sensing elements, results in detector output signals that are phase separated from one another. In other words, the comparator detector output signal 1318 a is phase separated with respect to comparator detector output signal 1318 b and likewise, precision detector output signal 1324 a is phase separated with respect to precision detector output signal 1324 b. As will be explained further in connection with FIG. 16, direction detector 1320 generates direction signal 1352 based on this phase separation between processing channels.

Because the comparator detectors 1302 a, 1302 b provide reliable respective output signals 1318 a, 1318 b promptly upon powering up the sensor, the direction signal 1352 based on such comparator detector output signals 1318 a, 1318 b likewise can be reliable promptly upon powering up. The time interval corresponding to “promptly” may differ depending on the particular sensor application and configuration. For example, in some configurations, the comparator detectors 1302 a, 1302 b may require some amount of rotation of the target before providing a reliably accurate output 1318 a, 1318 b, but even in such configurations, comparator detector output signals 1318 a, 1318 b are generally considered to be accurate before the precision rotation detector output signals 1324 a, 1324 b because of the time necessary to acquire the positive and negative peaks of the magnetic field signal.

Referring to FIG. 14, an example threshold module 1400 can include threshold modules 1400 a, 1400 b, each substantially identical and each associated with a different one of the processing channels. Thus, module 1400 a can provide the threshold module 1316 a of FIG. 13 and module 1400 b can provide the threshold module 1316 b of FIG. 13. For simplicity of illustration, only threshold module 1400 a is shown in detail and the operation of both modules will be described in connection with example module 1400 a.

Threshold module 1400 a can include a dynamic threshold module 1406 coupled to receive positive and negative peak signals 1404 a, 1404 b, respectively. The positive and negative peak signals 1404 a, 1404 b can be the same as or similar to the positive and negative peak signals 1328 a, 1330 a of FIG. 13, and can be indicative of magnitudes of positive peaks (P+) and negative peaks (P−) of the magnetic field signal 1332 a.

The dynamic threshold module 1406 is configured to generate a dynamic threshold value 1406 a. For example, the dynamic threshold module 1406 can calculate the dynamic threshold value 1406 a as a combination of the positive and negative peak signals 1404 a, 1404 b, such as a predetermined percentage of a voltage difference between the positive and negative peak signals 1404 a, 1404 b. A new dynamic threshold value 1406 a can be calculated from time to time or can be calculated when either one or both of the positive peak signal 1404 a or the negative peak signal 1404 b change in value.

In some embodiments, the dynamic threshold module 1406 is coupled to receive only one of the positive peak signal 1404 a or the negative peak signals 1404 b, in which case, the dynamic threshold value 1406 a is calculated based only upon the received one of the signals.

The threshold module 1400 a includes a memory device 1408, which can be a nonvolatile memory device, for example, an EEPROM. Memory 1408 can include a stored threshold memory region 1410 coupled to receive and to store various threshold related values, including a plurality of threshold temperature values, each associated with a respective temperature. For example, the threshold temperature values can include a first, “hot” threshold value indicative of a threshold value for the respective comparator detector 1302 a (FIG. 13) in a hot ambient temperature condition and a second, “cold” threshold value indicative of a threshold value for the comparator detector 1302 a in a cold ambient temperature condition.

A backup memory region 1412 can store one or more backup threshold related values including a plurality of backup threshold temperature values, each associated with a respective temperature. The backup memory region 1412 can store the threshold related values at the same or at different times than the stored threshold memory region 1410 stores threshold related values. Use of backup memory region 1412 to store backup threshold data can protect against data corruption, as may occur if the sensor operation is interrupted as the stored data is being changed for example. In the case where multiple copies of threshold related values are stored, each read operation may include reading each copy of the data and determining if any errors exist. For example, if three copies of the data are stored but one is different than the other two, the controller reading the data may presume the different data is unreliable and discard it. In another example, if a write operation fails because data read back does not match data intended to be written, then the write operation may be repeated.

Threshold related values can be stored in memory 1408 during manufacture and can be updated during operation of the sensor. For example, initial values can be programmed into memory 1408 at a factory setting or in situ by exposing the sensor to anticipated operating conditions during manufacture and/or during initial use.

Threshold temperature values 1406 b can be read from the memory 1408 by a memory/threshold controller 1420. In this way, upon powering up, the magnetic field sensor can use stored threshold temperature values 1406 b to generate a comparator threshold 1418 for use by the comparator detector 1302 a (FIG. 13) promptly upon powering up and at other times as will be described in connection with FIG. 15. Suffice it to say here that the controller 1420 can be coupled to receive one or more signals, for example, the stored threshold temperature values 1406 b, a power on-off signal 1422 representative of a power on or a power off of the magnetic field sensor, comparator detector output signal 1402 which can be the same as or similar to the comparator detector output signal 1302 a of FIG. 13, precision detector output signal 1403 which can be the same as or similar to the precision detector output signal 1324 a of FIG. 13, and temperature signal 1444 which can be the same as or similar to temperature signal 1346 of FIG. 13. In operation as will be described further in connection with FIG. 15, the memory/threshold controller 1420 can use the various inputs in a variety of ways to control the storage of the threshold related values in memory 1408 and to generate the threshold signal comparator threshold 1418 for use by the respective comparator detector.

Memory 1408 can also include a safety word storage area 1414 configured to store a digital bit or digital word indicative of a time when storage is ongoing in an indicated one of the stored threshold memory region 1410 and the backup stored threshold region 1412. Controller 1420 controls read and write operations of the memory device 1408 by way of a control line 1420 a, thereby controlling when storage occurs and other memory related operations.

The threshold related values can be stored in the memory device 1408 at a plurality of storage times, including at a storage time either at or immediately prior to a power down of the magnetic field sensor 1200 of FIG. 12 as indicated by power on/off signal 1422.

In some embodiments, optionally, the threshold module 1400 a can include a scaling module 1426 and/or an offset module 1428. The scaling module 1426 is configured to apply a predetermined scaling, and the offset module is configured to apply a predetermined offset to the comparator threshold 1418, providing an alternate comparator threshold 1428 a suitable for use by some embodiments of the comparator detector 1302 a of FIG. 13.

Referring to FIG. 15, a process 1500 is illustrated that can be used in conjunction with the threshold modules 1400 a, 1400 b of FIG. 14. In particular, with reference to threshold module 1400 a, the process can be implemented in part by the dynamic threshold controller 1406 and in part by the memory/threshold controller 1420.

The process 1500 begins at block 1506 by powering on the magnetic field sensor (e.g., sensor 1200 of FIG. 12). At block 1510, two or more threshold temperature values, such as a first, hot threshold value and a second, cold threshold value, are read from memory 1408 (FIG. 14). More particularly, in the case where multiple copies of threshold related values are stored in memory, reading the hot and cold threshold values at block 1510 may include reading each stored copy of the hot threshold value and each stored copy of the cold threshold value and determining if any such values differ from others, in which case the value(s) determined to be different may be discarded.

At block 1514, a computation is performed whereby a threshold value (referred to herein alternatively as the interpolated threshold) is determined based on the stored hot and cold threshold temperature values and the present temperature (as may be provided to the memory threshold controller 1420 by the temperature signal 1444 of FIG. 14). The calculation of the threshold may take the form of an interpolation or any other form of mathematical computation whereby the threshold is determined based on the stored hot and cold threshold temperature values. The calculation can be based on presuming a linear threshold response from the hot threshold temperature value to the cold threshold temperature value. It will be appreciated however threshold temperature responses other than a linear response can be used. It will also be appreciated that a threshold calculation based on more than two stored threshold values, each associated with a respective temperature, can be used to generate the interpolated threshold.

The interpolation calculation may be performed as follows: IF (THRESHOLDHOT>THRESHOLDCOLD) INTERPOLATED THRESHOLD=(THRESHOLDHOT−THRESHOLDCOLD)*(TEMPERATURE/n)+THRESHOLDCOLD IF (THRESHOLDHOT<THRESHOLDCOLD) INTERPOLATED THRESHOLD=(THRESHOLDCOLD−THRESHOLDHOT)*(TEMPERATURE/n)+THRESHOLDHOT

The threshold value thus determined by interpolation can be used at block 1518 by the comparator detector (e.g., detector 1302 a of FIG. 13) to generate the comparator detector output signal (e.g., signal 1318 a).

As blocks 1510, 1514, 1518 are performed, the precision detector (e.g., precision detector 1310 a of FIG. 13) can be acquiring the positive and negative peaks of the differential magnetic field signal (e.g., signal 1332 a) at block 1522. Once the positive and negative peaks of the differential magnetic field signal are accurately acquired (e.g., after a predetermined time has elapsed or a predetermined number of target features such as gear teeth have passed), at block 1526, a dynamic threshold can be calculated, for example as a predetermined percentage of the difference between the positive and negative peaks of the magnetic field signal. More particularly, in an embodiment, at block 1526, over the course of three consecutive teeth, the lowest P+ signal value and highest P− signal value are saved and then used to calculate the new dynamic threshold by averaging the saved signal values.

At block 1530, it can be determined whether the dynamic threshold computed at block 1526 differs significantly from the interpolated threshold value computed at block 1514. For example, it may be determined if the dynamic threshold differs from the interpolated threshold by a predetermined amount or a predetermined proportion or percentage of the magnetic field signal.

In an example embodiment at block 1530, the interpolated threshold is compared to the difference between the P+ signal 1404 a and the P− signal 1404 b once calibration has finished. If the interpolated threshold is found to be greater than 75% of the difference between P+ and P− plus P− (i.e., the dynamic threshold is more than 75% of the peak-to-peak magnetic field signal away from the interpolated threshold) or less than 25% of the difference between P+ and P− plus P− (i.e., the dynamic threshold is less than 25% of the peak-to-peak magnetic field signal away from the interpolated threshold) for a predetermined number of consecutive gear teeth pass the sensor (e.g., three teeth) and the difference between P+ and P− is greater than 100 G, there are no direction changes, and the temperature signal 1444 indicates a temperature between 0° C. and 100° C., then the interpolated threshold is determined to differ significantly from the dynamic threshold.

If the interpolated threshold and the dynamic threshold do not differ significantly, then block 1514 is periodically repeated, such as once per millisecond for example. If on the other hand the interpolated threshold and the dynamic threshold are determined to differ significantly, then it is determined at block 1534 whether the interpolated threshold has been stable for a predetermined period of time, as may correspond to a fixed period of time or a time corresponding to a predetermined number of set of sensed target features (e.g., gear teeth) passing the sensor.

Although not illustrated in the threshold generation and updating process of FIG. 15, once it is determined that the dynamic threshold differs significantly from the interpolated threshold at block 1530, the dynamic threshold calculated at block 1526 can be used by the comparator detector (e.g., detector 1302 a of FIG. 13) as the comparator threshold 1326 a to generate the comparator detector output signal 1318 a.

If the interpolated threshold has not been stable for the predetermined period, then block 1514 is again performed to generate the present interpolated threshold. If on the other hand the interpolated threshold is determined to have been stable for the predetermined period, then an update magnitude is calculated in block 1538. The update magnitude may be provided as a difference between the interpolated threshold calculated at block 1514 and the dynamic threshold calculated at block 1526.

In block 1542, updated quantities for the stored threshold temperature values are calculated based on the update magnitude calculated at block 1538. For example, updated values for the hot threshold value and the cold threshold value can be calculated by weighting based on the present temperature. As an example, the new, updated hot and cold threshold temperature values can be calculated as follows: IF (previous THRESHOLDHOT>previous THRESHOLDCOLD) THRESHOLDHOT=ΔTHRESHOLD+previous THRESHOLDHOT+(((n−1)−TEMPERATURE)/n)*ΔTHRESHOLD THRESHOLDCOLD=ΔTHRESHOLD+previous THRESHOLDCOLD−(TEMPERATURE/n)*ΔTHRESHOLD IF (previous THRESHOLDHOT<previous THRESHOLDCOLD) THRESHOLDHOT=ΔTHRESHOLD+previous THRESHOLDHOT−(((n−1)−TEMPERATURE)/n)*ΔTHRESHOLD THRESHOLDCOLD=ΔTHRESHOLD+previous THRESHOLDCOLD+(TEMPERATURE/n)*ΔTHRESHOLD where ΔTHRESHOLD is the update magnitude computed at block 1538 and ((n−1)−TEMPERATURE)/n) is an example weighting factor. It will be appreciated that other weighting factors are possible and various schemes may be used to determine an optimal weighting factor.

In this way, temperature response errors in the stored threshold temperature values will be corrected over multiple updates. For example, if the stored temperature response is flat (hot=cold) but should be slightly positive (hot>cold), then when the threshold is updated at a high temperature, hot will be updated more than cold, resulting in a positive stored temperature response.

In block 1546, the updated threshold temperature values are written to memory. As noted above multiple copies of the updated threshold temperature values may be written for example for redundancy purposes. Following block 1546, blocks 1510 and 1522 are again performed.

Referring also to FIG. 16, waveforms associated with direction detection by the magnetic field sensor 1200 including the controller 1300 of FIG. 13 include magnetic field signals 1332 a, 1332 b, each associated with a respective processing channel. Also shown in FIG. 16 are example detector output signals 1340 a, 1340 b (as may be provided by comparator detector output signals 1318 a, 1318 b at or near start up times and as may be provided by precision detector output signals 1324 a, 1324 b thereafter). Detector output signals 1340 a, 1340 b are processed by direction detector 1320 and output format modules 1314 a, 1314 b to generate respective sensor output signals 1350 a, 1350 b.

Various processing schemes can be implemented by the direction detector 1320 to determine the direction of rotation of the target based on the relationship of the phase separated detector output signals 1340 a, 1340 b. For example, one of the sensor output signals 1350 a can be provided as a two state signal that transitions every time either channel detector output signal transitions, as is shown in connection with example signal 1350 a. The other sensor output signal 1350 b can be used to provide an indication of rotation direction based on the phase relationship of the detector output signals 1340 a, 1340 b. For example, if it is expected that the first channel output signal 1340 a will lead the second channel output signal 1340 b, then a change in this phase relationship (e.g., as occurs at time t₂ following a change in the rotation direction at time t₁) causes a transition of the sensor output signal 1350 b, thereby providing an indication of the direction change.

All references cited herein are hereby incorporated herein by reference in their entirety. Having described preferred embodiments, which serve to illustrate various concepts, structures and techniques, which are the subject of this patent, it will now become apparent to those of ordinary skill in the art that other embodiments incorporating these concepts, structures and techniques may be used.

It will be appreciated that features shown in connection with the example embodiments can be used in connection with other embodiments.

Accordingly, it is submitted that that scope of the patent should not be limited to the described embodiments but rather should be limited only by the spirit and scope of the following claims. 

What is claimed is:
 1. A magnetic field sensor, comprising: one or more magnetic field sensing elements configured to generate a magnetic field signal responsive to a magnetic field; a detector coupled to receive an interpolated threshold and a signal representative of the magnetic field signal, wherein the detector is configured to compare the interpolated threshold with the signal representative of the magnetic field signal to generate a detector output signal; a memory configured to store a first threshold value indicative of a threshold value at a first temperature and a second threshold value indicative of a threshold value at a second temperature lower than the first temperature; a temperature sensor to generate a temperature signal representative of a temperature of the magnetic field sensor, and a threshold module coupled to the memory and to the temperature sensor configured to generate the interpolated threshold based on the stored first and second threshold values and the temperature signal.
 2. The magnetic field sensor of claim 1, wherein the detector output signal provides an output signal of the magnetic field sensor upon powering on the magnetic field sensor.
 3. The magnetic field sensor of claim 1, wherein the detector comprises a first comparator detector and the detector output signal comprises a first comparator detector output signal and wherein the magnetic field sensor further comprises a second comparator detector configured to receive the interpolated threshold and also configured to receive the signal representative of the magnetic field signal, wherein the second comparator detector is configured to compare the interpolated threshold with the signal representative of the magnetic field signal to generate a second comparator detector output signal.
 4. The magnetic field sensor of claim 3, further comprising a direction detector responsive to the first and second comparator detector output signals to generate an initial direction signal indicative of a direction of movement of a target positioned to affect the magnetic field.
 5. The magnetic field sensor of claim 4, wherein the magnetic field sensor further comprises: a first precision detector coupled to receive the signal representative of the magnetic field signal and to compare the signal representative of the magnetic field signal to a dynamic threshold to generate a first precision detector output signal; and a second precision detector coupled to receive the signal representative of the magnetic field signal and to compare the signal representative of the magnetic field signal to the dynamic threshold to generate a second precision detector output signal, wherein the dynamic threshold is based on one or both of a positive peak signal having a plurality of positive peak values representative of positive peaks of the magnetic field signal or a negative peak signal having a plurality of negative peak values representative of negative peaks of the magnetic field signal.
 6. The magnetic field sensor of claim 5, wherein the direction detector is further responsive to the first and second precision detector output signals to generate a precision direction signal indicative of a direction of movement of the target positioned to affect the magnetic field.
 7. The magnetic field sensor of claim 6, wherein the initial direction signal is used to generate a direction output signal of the magnetic field sensor during a first time after powering on the magnetic field sensor and the precision direction signal is used to generate the direction output signal of the magnetic field sensor during a second time following the first time.
 8. The magnetic field sensor of claim 1, wherein the one or more magnetic field sensing elements comprise at least three magnetic field sensing elements and wherein the signal representative of the magnetic field signal comprises a first differential signal generated as a difference between an output of a first one of the at least three magnetic field sensing elements and a second one of the at least three magnetic field sensing elements and a second differential signal generated as a difference between an output of the second one of the at least three magnetic field sensing elements and a third one of the at least three magnetic field sensing elements.
 9. The magnetic field sensor of claim 1, wherein the threshold module is further configured to generate, at an update time, a first updated threshold value indicative of a threshold value at the first temperature and a second updated threshold value indicative of a threshold value at the second temperature and wherein the memory is configured to store the first updated threshold value and the second updated threshold value.
 10. The magnetic field sensor of claim 9, wherein the update time occurs when a dynamic threshold differs from the interpolated threshold by a predetermined amount, wherein the dynamic threshold is based on one or both of a positive peak signal having a plurality of positive peak values representative of positive peaks of the magnetic field signal or a negative peak signal having a plurality of negative peak values representative of negative peaks of the magnetic field signal.
 11. The magnetic field sensor of claim 10, wherein the first updated threshold value is based on a difference between the dynamic threshold and the first threshold value and the second updated threshold value is based on a difference between the dynamic threshold and the second threshold value.
 12. The magnetic field sensor of claim 11, wherein the first updated threshold value is further based on a weighting factor and the second updated threshold value is further based on the weighting factor.
 13. The magnetic field sensor of claim 1, wherein the memory is further configured to store at least a third threshold value indicative of a threshold value at a third temperature between the first and second temperatures and wherein the threshold module is configured to generate the interpolated threshold based on the relationship of the measured value with respect to at least the stored first, second, and third threshold values.
 14. A method of sensing a magnetic field with a magnetic field sensor, comprising: generating a magnetic field signal responsive to the magnetic field; storing, in a non-volatile memory device, a first threshold value indicative of a threshold value at a first temperature and a second threshold value indicative of a threshold value at a second temperature lower than the first temperature; generating a temperature signal indicative of a present temperature of the magnetic field sensor; generating an interpolated threshold based on the first stored threshold value and the second stored threshold value and the temperature signal; and comparing the interpolated threshold with a signal representative of the magnetic field signal to generate a detector output signal.
 15. The method of claim 14, further comprising providing the detector output signal as an output signal of the magnetic field sensor upon powering on the magnetic field sensor.
 16. The method of claim 14, wherein comparing the interpolated threshold with the signal representative of the magnetic field signal comprises comparing, with a first comparator detector, the interpolated threshold with the signal representative of the magnetic field signal to generate a first comparator detector output signal and comparing, with a second comparator detector, the interpolated threshold with the signal representative of the magnetic field signal to generate a second comparator detector output signal.
 17. The method of claim 16, further comprising comparing a phase of the first comparator detector output signal to a phase of the second comparator detector output signal to generate a direction signal indicative of a direction of motion of a target positioned to affect the magnetic field.
 18. The method of claim 14, further comprising updating, at an updating time, the first threshold value and the second threshold value and storing in the non-volatile memory device the first and second updated threshold values.
 19. The method of claim 18, further comprising generating a dynamic threshold based on one or both of a positive peak signal having a plurality of positive peak values representative of positive peaks of the magnetic field signal or a negative peak signal having a plurality of negative peak values representative of negative peaks of the magnetic field signal, wherein the updating time occurs when the dynamic threshold differs from the interpolated threshold by a predetermined amount.
 20. The method of claim 19, wherein updating the first threshold value comprises generating a first updated threshold value based on a difference between the dynamic threshold and the first threshold value and updating the second threshold value comprises generating a second updated threshold value based on a difference between the dynamic threshold and the second threshold value.
 21. The method of claim 20, wherein generating the first updated threshold value is further based on a weighting factor and generating the second updated threshold value is further based on the weighting factor. 